1) get yourself a counsellor. As much as you may be able to talk to friends it is far too tempting to avoid admitting things so that they dont feel too much under pressure. With a counsellor you dont have to worry about them, so can tell them everything.
2) get yourself a box of things to make you happy. Pics of family, friends, some numbers to ring when youre feeling bad. A favourite teddy. Some paper and pens, chocolate, you get the idea! When youre feeling bad get this out, have a good cry, write down why you want to commit suicide, and why you want to stay alive. Whatever takes you at that moment.
3) Consider, are you seriously wanting to commit suicide. For years I considered it as an option, as a type of thing that I could do, but the negatives always outweighed the positives. Then something changed and it was only from that point on that suicide became a proper option. Which stage are you at? If youre at the second point, get yourself down to the docs, asap. It may be scary, it may be horrible, but you are important enough that you deserve to live,and so should give yourself a chance.
One of the best things I ended up doing, was getting a pact with someone. They got me to agree that before I tried anything again I would get professional help. It sounds stupid, but when the thoughts have come back, I have always found it a comfort knowing I cant do it until Ive gone for help.