I am not a trained professional. I cannot write a definitive guide on how to control the urge to self-injure. I suspect that even if I was a trained professional, I would still be hard-pressed to come up with such a guide. What I can do, is share what worked for me. If you are someone who struggles with this, I hope this helps. However, I would still urge you to get professional help.
1. Solving the root causeI want to start by saying that the holy-grail of conquering the urge to cut, lies in resolving the underlying issues that cause the urge. Cutting is a coping method. It satisfies a need. As long as this need exists, you will have a hard time controlling the urge to cut. Read more about his from my post Self-injury: what's that all about?. Obviously addressing that need takes a lot of time and work. You will need ways to cope in the short term.
2. Short-term measuresThere are lots of lists on the internet that will give you things to do instead of cutting - things like pressing ice-cubes against your skin to create the physical sensation, drawing onto your skin with a red marker, punching pillows, etc. I have found a good list of short-term coping techniques, categorised by the need they fulfil, at www.helpguide.org.
I felt numb a lot of the time. So numb, that there were times when I doubted my own existence. The pain of cutting created a clear sensation, and confirmed that I was real. I started wearing a rubber band around my wrist and when I felt like I was fading away into non-existence, I would snap it against my skin until it hurt. It created a physical sensation that was strong enough to bring me back.
Another strategy that I used often, was to call someone. Often, calling my therapist or a friend and telling them about what had triggered me instead of cutting, was enough.
3. The postponement trickIf all else fails, there is always the postponement trick. The idea is to postpone the act of cutting. Instead of trying to fight the urge to cut, set a time when you can do so. It should be far enough in the future to allow you time to gather your thoughts, but not so far that you become despondent and give up on waiting.
I'll do it in 15 minutes, or after I've finished what I'm busy with, or...
When the time came when I had planned to do it, more often than not, the urge had passed.
4. MedicationAnti-depressants helped to easy my need to self-injure. If you are seeing a therapist, you might want to speak to him/her about this. If you are not seeing a therapist, you GP might also be able to assist you. Whatever you do - don't try to self-medicate with alcohol or street drugs. Going this route will only add to your problems.
5. Take care of yourself, physicallyThe other thing that was very helpful for me, was learning to take care of myself on a physical level, and to take pride in my appearance. When I was in sober-living, I learned to eat well, to shave regularly, to keep my hair clean and tidy, etc. I cycled to work, making my body fit and well toned. I bought nice, short-sleeved shirts that made me feel good when I wore them, but that would also show any cuts on my forearms (my favourite place to cut and the main reason why I mostly wore long sleeves in those days). I got tattoos. The tattoos were especially effective in changing the way I felt about my body. It made me feel like my body was my own, and no longer belonged to my abusers. It made me not want to scar myself any more.
These are just some of the techniques that worked for me. If you are struggling with the urge to cut, these techniques might also work for you, or you might have to find others. Whatever short-term coping methods you find, I would strongly urge anyone who find themselves wanting to injure themselves to get profession help, with the aim of eventually accomplishing number 1 - solving the root cause. That is really the only long-term solution.