This is what I think they mean, I don't totlly believe all of them
1. What goes around comes around. = Your actions towards others will be reflected back to you either through that person or another person/ action.
2. The best place to hide something is in the open. = Sometimes if you hide something in a really obvious place people will think that it's too obvious of a place and will never look there.
3. Be careful what you wish for...you might get it. = Sometimes when you are feeling very powerful emotions you may say something you really don't mean because your emotions have taken over. So you may regret saing it.