Training is pretty set and forget, at least for me... I didn't even set up custom schedules until several seasons in- have 5 now (Def, DM, MC, AM, ST).
FM12 is the first one I've played so others here probably have better advice, but building up training facilities, coaching, and scouts ASAP is what has let my team improve the most, I think. I have scouts in areas that seem to get me a high number of quality regens and manually make my scouts report on everyone under 19 and worth at least 380k. I generate a lot of young talent which generates both future starters and future transfer money. My facilities are "state of the art", but I seem to have to do some construction every year to keep up with it. Coaching, I hired/fired a lot my first few seasons. If I could find someone who would increase the training category even half a star, I'd mutually cancel someones contract to make room.
Other than that, getting used to how/what the tactics do makes a pretty huge difference, but that's hard to explain simply.
