I think an 18 month old is too young to pick up toys by himself. You'll defnitely have to tell him to do it for a while, and you'll probably need to do it with him as well, at least until he's 2 or 3.
My philosophy with child rearing is that I'm training their hearts, not their behavior. As a Christian, I want my children to do good things because they're pleasing to God--not just because of fear of punishment, a mad mom, or something like that. Anyway, since they don't really have much of a conscience when they're little, our rules right now are the basics, designed to keep them safe and make our house a happy place to live. We'll start making rules that aren't quite as important when they're old enough to understand that other people have feelings and that doing things that make God and other people happy is important.