I use a rasp and I learned basic skills from 20 years or so of watching farriers trim, and increased my knowledge with wide reading and instructional DVDs.
A rasp which is replaced whenever my EP throws one out the back of the van, and a handheld sanding block with fine sandpaper wrapped round it to polish if needed. Taught myself really but EP checks and guides me as my back doesn't allow me to do all of them all the time, due tomorrow actually and i haven't touched any of them for a couple of mths so may be an expensive visit........
Did a three day "hoof care for owners" course including dissecting and trimming cadaver legs After that, started doing basic maintenance supervised by my trimmer at the time, then gradually took over. Did loads of reading and research...
And now the horse trims his own, with the help of the local lanes and roads It's been 4 years, I think, since we saw trimmer last. (I help him out with the occasional mustang roll, but to be honest, he does that himself, and there's never a single chip or roughness on the hoof wall). I do check balance and wear regularly (well, every day when cleaning hooves, to be honest), but my rasp and hoof knife sit in a warm dry cupboard, making appearances every few months and then getting put away again mostly unused Use a proper (SaveEdge) rasp and a right handed hoof knife which I sharpen as required.
My trimmer has taught me, I've only just started though so still on a learning curve, I use a rasp and a knife (only for the bars if needed). I plan to keep having my trimmer out every 3/4 months to check what I'm doing.
With one horse I'm finding it really easy, she has simple feet. My other is new to barefoot and is an ex-racer so has typical long toes and low heels so I'm going very slowly and carefully with him and will prob get my trimmer out soon to make sure I'm doing it right. My only concern with him is how his feet will change and when will his toes start to shorten. He had the winter off work and I've just started him again last week so I'm barefoot rehabbing him at the same time... it's going to be a long slow slog and all the wet ground isn't helping.
On a plus though, he walked out to the field the best he ever has this morning so looks liike I'm going in the right direction!