I hope its not your objective to generate comments. I am not an expert (under 200 karma) but will advice anyways :-

1) Ask something when you need help and its not something obvious. Googling on your question before posting might help. For example, "What is the search engine you guys use ?" is a bad question.

2) Show something when you have something worth showing. Many people here are creating something and they like seeing what others are creating. If you are proud of something you built, show us.

3) People usually tend to contribute to a discussion when the original author seemed to have done some research himself. Take the "Brag HN" thread for example, I wonder if the author hadn't posted some examples about what kind of "about you" he wants to hear, it would have generated so much discussion.

4) Lastly, follow your instincts and have fun.