I would suggest that you find and read some of the guides to the characters and pick a class you like. You might well consider, as I did, a class that is good for soloing to start with. Why? Well, I went in fairly cold and knew I'd be spending time alone. A class that is good at soloing will always help there, because you can learn the ropes with a character that is likely to survive pretty well in most situations. That said, if your temperament suits a class that isn't really designed for solo play well, you will probably do well with that as your first class too - there are classes which are more suited to solo adventure but all of them do well enough and enjoying it more important I suspect. You will, of course, make mistakes with the class, but although the people that are grinding as fast as possible to 70th Level (or 80th soon) might laugh at what you do, the mistakes you make (learning skinning and missing the leatherworking trainer so my leatherworking is about 100 points behind skinning, D'Oh) aren't going to cripple your character in the longer term, they just mean things will take longer to achieve - but then you're learning a new world so there's learning time to include too, isn't there?
The skills system seems bewildering at first. You have some class skills - weapons, spells, things like that. You probably have some racial abilities - Forsaken all get cannibalism that lets them heal by eating humanoid corpses for example; Night elves all get a weak hide ability. You can then have two primary professions - but some are harder than others: enchanting is a hard one to get started on for example - and some make sense to learn together: skinning and leatherworking, mining and blacksmithing, herbalism and alchemy make nice pairs because you gather the raw materials (or most of them) with one profession and convert the resources into products (and usually more money) with the other. In addition, some skills make sense for certainly classes. Rogues can only ever wear leather armour (I think) so skinning and leatherworking is a good set for them - but so is mining and blacksmithing since that will let them make their own weapons. In addition, everyone gets access to three "secondary professions" First Aid, Cooking and Fishing. They are all good - you make bandages, cook the fish and meat you get from fishing and your kills, and catch fish with them. Food will help you heal, and make you money. Cooked food more so. I've started to get used to it, and now I'm hitting the fact I can't improve my cooking, nor my first aid without quests. Oh well. That leads neatly on to...
The quest system strikes me as good and bad too. It offers you a history of your race at first, which is a lovely touch. I might well do the starting quests for all the races just to find out the lore. You will quickly realise you should collect quests because often you can complete several at once. Experienced players will recognise the location in the picture of me, at about 32nd level. There are about 8 quests available at my sort of level there. However, five them basically say "walk around the salt pan and collect things" (1 from static "treasure" 4 from things you have to kill and harvest) so if you can, as I did, do all five at once rather than one at a time, it is a lot quicker and easier. The quests also nicely move you around the world, as well as sometimes teaching new class skills (hunters have to do a "pet quest" at level 10 to learn how to summon, control and feed their pets for example). That said, there are a couple of odd things - why can I only have 25 active quests at once? Who decided on the levels for the quests? Some you can easily complete at a far lower level than indicated. Some I still can't do safely several levels higher than indicated.
Having mentioned the good points, why is the quest system bad? Well, it can be very linear and lack any sort of obvious logic. If I kill the monster on a quest it may drop a given item. If I kill it at other times it won't. I'm currently doing a series of big game hunting quests, and each time I finish one (or all three in the "family" if I'm smart) I have to go back and renew the quests for the next step in the family. Annoying. That said, some of the quests tell great stories and are well worth it, as long as you don't mind running back and forth a bit.
The final thing - add ons. I still describe myself as a Second Lifer, rather than a MMORPGer. Although the UI of SL can be hacked, it is an effort (at the moment). However there are a range of attachments you can buy, and that I use, from collars, to HUD radars, to Salamander HUDs. In World of Warcraft the options aren't quite the same but... various people have made various tools to make your life easier. There are hundreds of add-ons, possibly thousands, although they don't all work well I must say up front. But, the ones that do are wonderful. For example, I use a recipe radar. It pops up on the minimap a scroll indicating the direction of any vendors with anything of interest in your region. It also shows their name, how many recipes they know and how many are of use to you. There are loads of others - with my hunter for example there are rows of buttons available, and which I use, which display my tracking, trapping and aspects. Why is this good? Well I hide them on the edge of the screen where they don't take up too much room and I can quickly and easily change aspects, set traps and change what I'm tracking. Of course the fast bar lets me do this too, but this way I have a "ranged combat" bar with various stings, strikes, aimed shots and so on, plus feign dead and flare just in case. My melée fast bar also includes feign dead, plus the various melée attacks. Skillet is an add-on that lets you see your craft skills differently, plus lets you queue several recipes in a row, then visit a vendor and purchase all the buyable ingredients they have with a single click. Building lots of leather goods after a good hunting trip? Excellent news, you can buy all your threads, salts, dyes etc. with just one click! It makes life a whole lot easier.
Will I stay in World of Warcraft after my free month? I don't know to be honest. That's not really a fault of World of Warcraft, as MMORPGs go it is a good example of its type. It's more about me. I still play table-top RPGs and I just plain prefer that sort of approach. Even on a role-play server World of Warcraft isn't role-play the same was as a table-top game with other good players can be. But if you're considering dipping your toes into World of Warcraft for the first time, don't be scared. You can learn, have fun and still be a good character when you get to 70th Level. You might not be the best possible ever, but you can be good, and have fun getting there.