I have a love of asking questions. I find that the best way to build up a system or character is to ask a question about it (such as "why are all magic wands wood?"), then work and find an answer ("woodworking/carving is very important in this culture.").
If you describe something to me, I will ask as many questions about it as you want. If you want a specific kind of question (such as "ask about their past") just tell me.
This is one of my favorite things to do, so don't feel bad if you need a lot of questions, or have specific guidelines! :)