I agree with Mike that a baby sweater is a good place to start. You'll never hear a baby complaining that his sweater doesn't fit just right or that it makes him/her look fat.
Also you can learn the things to do without having to do so much knitting.
With a baby or adult sweater-- look for something that looks easy. Read through the pattern and see if you know how to do everything called for or almost everything. Don't try to do everything on your first attempt. I'd go with something quite plain and basic. Then once you've been successful on your first one you will be ready to add some other features to the next one. Keep building skills and soon you'll be ready for most anything.