Well my father was a heroin addict and the one thing i can tell you right off the bat is not to get methadone treatment unless it is a last resort. If you thought heroin was addicting and had painful withdrawal methadone is much much worse.
That being said the best way to truly get off the drug is two fold, first prepare for the withdrawal. You have to actually plan to be very very sick and such. Try to have friends or family at call or with you through this process so they can help you out through out the day. But know that the withdrawal you feel is very temporary. I know personally that with my Father it only took him 1 or 2 days to get them to go away completely. If you start to feel really bad, do not hesitate to go to a hospital, they should also be able to help you through this very difficult time if you need that much help. Second, and this will probably be the hardest part, you need to get away from the people you know who also take heroin. This will help stave off the mental addiction. If you need to talk about this, feel free to pm me anytime