This comes from Mind website
There are lots of things you can do to make a difference to someone you know who self-harms. Your attitude and how you relate to them is one of the key things that can help them feel supported. Here are some things to keep in mind:
Try to be non-judgemental.
Let the person know that you are there for them.
Relate to them as a whole person, not just their self-harm.
Try to have empathy and understanding about what they are doing.
Let them be in control of their decisions.
Offer to help them find support (see Useful contacts).
Remind them of their positive qualities and things they do well.
Try to have honest communication, where you take responsibility for any fears you have.
Having friends I could ring up and talk to about everyday things gave me some respite from the despair.
What doesn't help?
Sometimes, even with the best will in the world, attempts to support someone can backfire. Here are some potential pitfalls to watch out for:
Trying to force change.
Acting or communicating in a way that threatens to take control away from your loved one.
Either ignoring their injuries or overly focusing on them.
Labelling self-harm as 'attention seeking'.
Although it often isn't, self-harm can sometimes be a person's way of asking for attention. If so, it is important to remember that there is nothing wrong with wanting attention, and that deep distress can get in the way of someone's ability to be direct about what they need.
Take care of yourself
Supporting someone who is self-harming can be a long process with many ups and downs. Taking care of yourself will enable you to stay involved for longer and to keep well. See How to cope when supporting someone else for more information.