
start with some still lifes... i know it's cliched, but start with a bunch of bottles. It quickly becomes apparent that most things back be drawn by breaking them down into smaller, simpler objects. I'm not particularly good at the whole art thing, but you should have seen the crap i drew before.
Also, you may want to start with charcoal. It's cheap, and it's messy, and you can't really get the definition you can out of pencil, but it lets you focus on getting the shapes right.