1. Learn and use your new spell rankings
I cannot stress this enough. It is incredibly frustrating to find out that your last hour of killing elementals would have been substantially easier if you remembered to use you new rank of frostbolt. They auto update on your toolbar now as you learn them, but this is only the case with the talent spec you have active at the time of learning the new spells, so if you have dual specs, make sure both are covered.
Also, this goes double for your non-combat spells; your teleports, portals, food and water should all be learned as soon as is possible. Don't forget the teleport and portal to Stonard/Theramore at level 35. These are part of the benefit of being a master of the arcane, so ignore them at your own peril, or at the very least your increased inconvenience.
However, this doesn't mean that you need to have all of your spells on your toolbar at all times. Let the portals stay in your spellbook for when you need them, or just pick one or two you use consistently to put on a secondary bar. Likewise, if you are specced frost, don't leave arcane missles in the middle of your useful spells. Either take it off completely, or push it to the side for the one time you run into a frost immune mob.
2. Choose your talents before you select your talents
What I mean by this is that it is in your best interest to use the talent calculator on WoWHead or on Blizzard's own site to see what is possible before you choose in-game. Also, look around online or inspect people in town to see what builds are popular, or at least to find the few talents that are a must have. It helps to have a goal rather than just putting points in whatever sounds good at the time, especially in order to get the higher end talents which are where your real benefits are. Likewise, it's best to pick a tree and stick with it, at least until you get to the end of the tree, then you can decide to fill in the rest of the tree or split off.
As far as picking a tree goes, assuming you haven't picked up Arcane Blast yet, Arcane isn't much of an option, so that leaves Fire or Frost. I have had good luck leveling up as both, but Frost is substantially easier. Between such gems as Ice Barrier, a friend, and the awesome-ness of chilly blizzards, it is pretty easy to skate through the mobs without breaking too much of a sweat. Likewise, your talents to help you hit and decrease your mana costs will help you put out consistent damage and be able to keep it going. Fire, on the other hand, is a lot less defensive, and so you will end up face down more, but when you are on top of your game, you won't see higher numbers pop out of your enemies heads with any other spec. So pick either of them and enjoy watching everything around you go boom.
3. Glyph appropriately, and often
When you level up and make the mad dash to grab your new spells and spend your talent points wisely, it is easy to forget to fill up your new glyph slot as well or to replace a low level glyph with a better one. Some glyphs are good no matter what, and all leveling mages should get them, while others are more dependent on your spec and what you need at the time. If you are looking for a bit more guidance, again, check around online or people in town and see what they have. The only problem to this is that the raiding glyphs might not be what you need to help you survive a solo mob pull gone wrong. That's why it is in my opinion to glyph for survival/utility until you are level 80, or nearly there, then worry about glyphing for instances.
4. Pick your professions based on your needs
There is two ways, as far as I can figure, to picking your professions; you either pick them to make money, or to make your character more powerful. Don't get me wrong, you can do both, but that isn't going to happen prior to you getting maxed out in your character's level and your profession's level.
To make more cash while you are out in Azeroth killing things and taking their stuff, you can go either of the dual gathering routes with mining/skinning or herbalism/skinning. It is hard to go herbalism/mining as you can't track both at the same time, but with a well filled out gatherer, you can try to, it just gets more complicated and I wouldn't recommend it for a new player. You can find out on your server's auction house what brings in more gold, herbs or ore, and then go with that one, but remember that can change very easily after a patch or two. I my experience mining has always made me a bit more gold than herbalism just because there are three crafting professions that need ore; jewelcrafting, blacksmithing, and engineering, where there is only two professions that need herbs. Assuming there are equal numbers of all the professions, this means there will be 33% more people in need of your ore than herbs. This is some very fuzzy math, granted, but it gives you an idea of what to expect.
On the other hand, if you want power and you have a friend that is funding your new character or you have an established character that you can have invest in your new mage you can go for one or two of the crafting professions. While you are still leveling up, it is a good idea to have one crafting profession and the gathering profession to go with it, since you will be walking by all of those mining nodes/dead animals/growing bushes anyway. I will do a quick rundown of all the optimal combinations, and how they would work for a power-hungry mage:
- Alchemy/Herbalism: Makes keeping a stack of health and mana potions on you trivial, as well as giving you access to some potions to keep you alive longer or buff your spells. By end game you become a master of a certain type. This means you have a chance when you make something (an elixir, a potion, or when transmuting something) that you will make extras. Basically a nice way to get some free things to either sell, give to guildies, or use yourself. However, no matter which mastery you pick, you can still make and transmute everything at the time of this writing to the best of my knowledge.
- Inscription/Herbalism: Makes it easy to keep up-to-date with your evolving glyphs, and might be able to make yourself a bit of gold providing glyphs for others. Scribes can also make for themselves some nice off-hand books which are nice for when you find yourself with a nice caster dagger or sword and nothing to hold with your left hand. Can also make tarot cards for quests dealing with the Darkmoon Faire, which people will pay nicely for, and you might be able to snag yourself a decent item or two keeping the cards for yourself. In end game, you can enchant your own shoulder items, which will save you some gold and time in grinding reputation with some of the factions of Northrend. I should also point out that scribes make vellum for enchanters to hold their wares in stasis to they can be sold on the AH. This is a decent way to get some funding as well, and it does make it possible to make a enchanter/scribe, but you will still need some way to get herbs to make your inks, so it might be something you want to swap to when you reach level 80.
- Blacksmithing/Mining: This does nothing for a mage until high levels when they can get two more gem slots. Its not worth it to drag this anchor with you while you level, so pick up blacksmithing at end game if you need the extra gem slots so badly.
- Enchanting/Tailoring: This is the combination you will see a lot of, as neither of these professions have a gathering profession to go with them. Tailoring just needs the cloth you get from looting humanoids, and enchanting uses the materials you get from disenchanting magic items, which does include those that you make from tailoring. Tailoring is clearly useful for mages since we can only wear cloth. This alone will allow you to keep you gear updated for relatively cheaper than buying armor off the AH, and without the problem of needed to run instances over and over for a low chance drop. Also, at higher end tailoring you pick a mastery similar to alchemy. You get a chance to make more of the respective cloths and you are able to equip certain items based on your choice. For now, its seems that Shadoweave items give you spellpower, stamina, intellect, and hit, and is ideal for a mage. Mooncloth gives you spellpower, stamina, intellect and spirit, which isn't too bad for mages either, but not quite as nice. Lastly, Spellfire gets you intellect, spirit, spellpower and haste, which is more for healers, so mages can safely pass. Enchanting is a good way to make some cash in the end game, although it is a bit harder to get people to drop their gold on mid-range items since it is bound to be replaced soon thereafter. Nonetheless, it is still a good way to keep your gear in tip-top shape, and it can also help make up for other items that may be lacking. This is always a good choice for mages that don't want to just gather materials for everyone else.
- Engineering/Mining: Engineering is the one profession that is more fun then useful. You get some really nice toys to play with, but most of the best ones require you to have engineering to use them, so there isn't much selling available. You get access to some trinkets, which can make those slots a bit easier to fill, and some random items, like boost power, and extra vanity pets. Basically, engineering doesn't do anything for mages that it doesn't do for everyone else. That said, some people still swear by it if for nothing else than it is one of the more entertaining professions out there, but if you are looking to max out your mages potential, you should probably look elsewhere.
- Jewelcrafting/Mining: Another solid combination, although this one isn't specifically for mages like tailoring is. Jewelcrafting lets you fill your ring and necklace slots substantially earlier than others, and although you could buy them off the AH, it does save you some gold making them yourself. As you get further along, you get to cut your own gems, which can be a very profitable venture, especially if you are finding your own gems through mining. At the end game, you are allowed to socket Dragon's Eye gems in three of your slots, which give a substantial bonus over the regular epic level gems. Well before end game content though, jewelcrafting is an easy way to fill in spots your gear is lacking. Don't quite have your hit capped? A Rigid Autumn's Glow or two will fix that. Hot Streak's not firing up as much as you like? Slap a few Potent gems in there to fix that and to have huger crits at the same time. As I hinted at above, when you do finally hit end game stuff, and you no longer are taking the time to mine as much as you used to, dropping mining for blacksmithing for the two extra slots has shown to be highly beneficial for mages, but nothing that you need to worry about when you are still fighting the dinos in Un'goro.
- Leatherworking/Skinning: Another one that does little to nothing for mages. At high ends there is the fur lining that can be handy, but there is not enough in the middle levels to make it appeal to a mage still trying to reach the level cap.
All in all, this should be enough to make you dangerous out there. If you take nothing else away from this keep at least these three things in mind:
For the TL;DR:
- Spec for survivability/consistency when leveling. This normally means taking the Frost tree spec for Ice Barrier, the Water Elemental, and the mob slows that come with cold damage. Also take the glyphs that make leveling easier, Glyph of Evocation for instance.
- Choose your profession based on what you need. Just need gold? Go skinning with either mining or herbalism, and sell everything you grab. Don't need the gold as much as the bonuses or making leveling easier, then either do enchanting/tailoring, mining/jewelcrafting, or alchemy/herbalism.
- Keep your vision clear. Keep everything you don't need off your main tool bars. Remember, you are very squishy, so you need to be aware of all the mobs around you that could crush you into magical paste in no time flat. It also helps to have an escape plan for when you start to run low on mana and not on things that are angry at you.