It all depends what your trying to help them with. Sucide and thoughts of hurting themselves you diffently want to tell someone. Drugs or alchol its hard to help them when they don't want any help. Just be there for them. You do things that will make them mad they will resist what your doing. Good luck
Being one of those people I guess whoever you're talking about would see help as a sign of weakness so all you can really do is let him or her know that he or she can always come to you if they need you.
generally you can't. there is an old saying : - "you can lead a horse to water, but you can't make it drink. " - meaning: that you can help someone over, and over, teach them the tools and skills they need, but if they are unwilling to do it for themselves, they won't.