[csytan]

I self cut and fade at the edges, but I think the keys to doing this correctly are:

1. Good visibility of the back and sides of your head. Either a 3 way mirror, or some kind of video setup with your phone and a laptop.

2. Patience and practice. The muscle memory and hand eye coordination needed to handle the clippers correctly takes some time. If you cut your hair once every couple of weeks, that's approximately 25 reps per year, which really isn't that much considering the spacing between reps is so long.

Edit: I missed that you have been doing this for 12 years. That's longer than I've been at it ~3 years.

Another thing that helps is watching YouTube vids of legit barbers. There are a ton of different techniques that accomplish the same thing, you might find some new insights into ones that work for you.