It has to be high quality content and you'll definitely need some high quality back links, but yes, frequent updating is the key to frequent spider indexing.
In my experience, frequent updating (as Xemion said) does attract spiders. Also, having your links posted at forums and blogs can help.
do you mean a FAQ? or a actually, someone ask a question and you reply on the website? either way, The best way to go is write HQ content and get some good backlinks as Xemion said... Good Luck...