Oh, and for my first attempt (which ended in my giving up on the game shortly after the tutorial), I wish I'd known the dnd 2e rules. http://www.gamefaqs.com/pc/75251-baldurs-gate/faqs/8566]This
document[/url summarises them quite nicely from the point of view of the games, and I highly recommend reading it, if only to understand what I say next.
If you don't want to risk ending up with a useless character, and are planning to dual class at some point, look around online a bit and find out whether it's a sensible choice or not, and when is a good time to dual. You do have to be planning to dual class to something else from character generation to get the right stats high, so decide before starting the game if you plan to dual or not.
In particular, never dual class from a caster to a non caster, as non casters gain a lot of their benefits only if your early level ups are in their class. The big increases to hit points, for instance, only occur for your first 10 levels in any class, and if you spend 6 of those levels as a mage (who has poor hp) then switch to a fighter, you'll have lost over half of the big increases you could have gained, which is a significant part of the class. Casters, on the other hand, need to keep levelling to really be competitive against stronger enemies, as they unlock more and better spell slots.