I've always bitten my nails and the skin around them. I have been trying and failing to stop for years.
From about 13 I went through a face of obsessive eyebrow plucking for several years. It was ridiculous; I used to pluck my eyebrows too thin, then where I caused irritation there would be little swellings and spots, then I would pick at them causing sores. I basically replaced the lower part of my eyebrows with sores. It was a huge source of shame and misery.
Fortunately I managed to move on from the eyebrows thing, I keep them nice now - but unfortunately mainly because I began general face picking and touching. Funny I never really thought of it as the main problem (rather I just thought of it as the reaction to my real problem: simple acne), even though on looking back it clearly was (most sores/lesions on my face at any one time were/are there because I have opened them/ maintained them by picking).
Fairly recently I tried to stop biting my nails by putting on false nails. Initially this was successful - and suddenly it triggered me to realise was just how much I go to my nails, just automatically. Normally I guess I would have just nibbled them and thought nothing of it, but the presence of the false nails made me aware. I realised I was constantly aware of my fingers and nails, constantly drawn to touching and inspecting them. Then I sort of realised exactly the same thing was going on with my face.
So in a way that was good. But the downside was I developed a new obsessive habit. To get the false nails to fit better, I started pushing back the cuticles. This rapidly transformed into ruthlessly cutting, biting and peeling them. For a time this completely replaced my old habit of nail and skin biting. Then as I've tried really hard to get over the cuticle thing (with some success though I've not completely stopped it isn't too bad), nail biting has returned so I'm stuck with both. Weirdly the skin biting hasn't returned. I guess my taste for flesh has been satisfied by my cuticle destruction.
Now I am just sick of it. I desperately want to stop but I don't trust my efforts any more. Mild success with replacing one bad habit with another has recently led me to try obsessively washing and moisturising my hands as better alternative for biting/picking them. It has partially worked, but I don't feel any partial success is real success - if I don't completely stop I think I will go back to it.
I am making slow progress with my skin. One things which helps is that I don't cover it up (with make up) when I'm at home. This was a big step as I find my skin extremely embarassing uncovered. On the contrary, revealing my skin to friends and family has made me feel less ashamed (everyone including me just gets used to it), and less desperate to physically remove the problems (like spots, scabs) but trying to pick them away. I don't feel able to do the same thing at work because I just think it looks so unprofessional.
I would really like to find a mentor on TSR (perhaps in a skin picking society) because I want to stop, I think I need someone to help encourage me and make me feel good about it. One thing that puts me off trying to stop is it makes me feel even more guilty and ashamed, and then I seem to fail anyway. I'm just not sure how to change it all by myself.
I don't know if I could give advice to other people, as I've obviously been no good at stopping myself.