It depends on what needs deciding and whether or not I actually care about it. Obviously, the big decisions - like what I'm going to study, long-term plans, etc - I'll make by myself, usually off my own back with no input, unless I'm offered professional advice or something. But small things, like what to have for lunch, I'll usually let someone else decide for me, because I honestly don't care one way or the other. xD
If I'm by myself, I can be terribly indecisive, especially when it comes to buying things...of the choice between two things, I'll often pick the third option and not buy either, then leave feeling distinctly annoyed with myself. xD