Well, you can use Twitter in many different ways. You can tweet actively, you can just follow, perhaps you only like retweeting, perhaps you like engaging in discussions. Pick your choice! Personally I don't tweet much but I follow a lot of interesting accounts, and I like retweeting when they have good stuff I want to share. Sometimes I might also engage in discussions, but not often. Mostly I treat Twitter as a great information source though, with lots of amusing bits in between. Twitter is also a great service for getting updates for a lot of other services.
There's at least two accounts you might find interesting: @IsHL3OutYet and @ZhugeEX (whom you might also know from this site). I also follow a few interesting tech-oriented accounts, but I'm guessing they go a bit too deep for most people...
EDIT: Oh, hashtags. Right, I forgot. Just use them when you feel like they're somehow relevant, or not if you don't want to. They don't really matter, but you can browse tweets by hashtag, so if you use a hashtag, people can find your tweet more easily. You might want to check out the hashtag #ff, which stands for Follow Friday. Basically on Fridays, people recommend accounts to follow by using that hashtag. Who knows, maybe you'll find an interesting account to follow?
