These are my rules. Pretty obvious stuff, but I catch people not following them all the time despite that.
Be really super honest.
Be yourself, completely unwatered down. If they can't handle you that way, they don't deserve you.
If they ever abuse you in any way, kick them to the curb.
If they lie to you all the time, get rid of them.
Don't put up with ridiculously jealous people who try to make you stop being friends with all kinds of people you've known and loved for much longer than they've been in your life.