Well first of all, to those that say everyone who plays Warcraft is a loser, or has no life...I'm afraid they are sorely mistaken. It's all about how much you let the game take over. I've been playing it for over a year, and I still maintain all real-world relationships just fine. It's fun game, just always make sure, as was said in a previous post, you take it in moderation.
Now, as for how to pick a character you would like...You can read the description of any race and class on the right hand side of your screen when you select them. There will also be a description of racial abilities and bonuses there, which will help you decide what is best for which class. Of course, you can always make something that just looks cool, but if you want to get the most out of your character's utility, it's very helpful to look carefully at the racials in regards to what you want to do.
For example: if you want to raid and do dungeons as a caster, your best race is to go blood elf. This is because of the Arcane Torrent racial, which instantly restores 10% of your mana pool when used. It's on a 2 minute cool down (meaning you can use it every two minutes), and also silences nearby enemies.
if you want to pvp as a caster, a human is a good choice, so in a gnome or undead. Draenai are also viable because they have a heal ability that can save you in a tight situation.
There are many different combinations for the best of your class, depending on what you find most preferable to play. Try checking the World of Warcraft forums if you want help, or just Google your class and see what race people tend to play it as.
Factions used to be a limiter on this game as well, but since faction changes opened up a little over a month ago (I think), you can now play characters from either side on one realm, so it doesn't particularly matter, except to know that while you are playing one, the other faction will be aggressive to you (on a PvP server...NPCs are the only ones from the opposing faction that will be aggressive to you on a Normal server).
Hopefully this was somewhat helpful.
Characters I own (if you want help once in game) are:
Missmoon and Seraphian of Drak'Tharon
Iofiel and Arafael of Magtheridon