It depends. You really just need to spend more time reading the forums - especially the Alt Coin Announcements section. Some airdrops require nothing other than your address, some are a bit more involved. Every project is different. Once you've been around awhile, though, you'll get the hang of what is required. Most, though, do require you to have your account at a certain level - you'll need to increase your activity. Make insightful and constructive posts, though, otherwise they'll just get deleted.