Today is all we have. Yesterday is gone, tomorrow may never come, life is strange, wonderful and painful. Pain hurts, but we hardly ever die from it.
Don't ever give someone everything you have.
Don't ever take somebody back that fucked you so bad the first time around.
Don't be made a fool of.
Don't think you are special.
Don't think you know somebody because chances are you probably don't.
Don't think someone is your friend when they really just use you.
Don't trust those who you think you care about.
Don't let others talk down to you and call you a "fake", when they are actually the fake themselves.
Don't give up something in your life you are happy with for something that you know won't ever be, but have to find out the hard way anyways -- I can tell you now it isn't worth it. Hapiness is everything.
Don't ever think that nice guys finish first, they certainly don't.
Don't ever let someone get the best of you.
Don't live life thinking what if, what could of been.
Don't care about those who think nothing of you.
Don't let yourself get lead on.
Don't take those back in.
Don't let yourself rehash old feelings, you're just fucking yourself.
Don't give anybody but yourself the benefit of the doubt.
Don't care more about others than yourself, especially when to them you mean nothing.
Most importantly...
Don't make the same mistakes I made (all of the above).