I think contest is good.
create a creative contest like I created 2 days ago. I asked a question related to common sense and put bounty on it so that everyone could get benefit from it.
but sometimes giveaway is also better because it motivates those who are never able to give right answer.
in contest you can create puzzles (For example I play chess so I can create a difficult situation and can ask for the solution or for the best move)