Mainly art.. whether it's drawing, painting, music, etc. If you're not particularly artsy (like myself, can't paint or sing to save my life lol) then collecting art from others and enjoying it can be soothing, too.

The thing about expressing pain for the sake of validation, is that words should be enough. You should be able to tell people who are close to you that you are hurting, and they should take it seriously. If that's not the case, then for whatever reason(s) the people in your life don't want to deal with your hurting, so they're not going to respond to you cutting, drinking, etc if they can't handle responding to your words. They're just not going to really respond, period, beyond an initial shock factor, possibly, but then they'll stop responding.

So in some cases it's a matter of coming to terms with the reality that the people you wish would act like they care, simply are not going to. Damaging yourself in various ways doesn't solve this problem. It's a problem that cannot be solved, so it's important to come to terms with it, even though that might be extremely hard.

But when it comes to expressing your emotions to yourself and for yourself, I think various forms of art is the best way to go.