Well I always had my problems with finding true friends, too.
Especially when my parents had their problems with each other I tried to avoid these "stupid people in puberty".
I can't really say why, but then I just decided to trust those I had sympathy fo and my feeling about people luckily rarely betrayed me, I think becous I watched at the people for a while before I decided to trust them.
I don't think that there is a trick... You have to find people you like and get to know them and if you still like them then, you have got a new friend. Otherwise you haven't revealed erverything to a stranger.
I myself only go as far as I feel good with it.