When I lived in San Diego, I played golf year around. I tinkered with my swing quite a bit while I was there and one book I found interesting was Tour Tempo, by John Novosel and John Garrity. It was a very interesting concept and it improved my swing.
The idea is that every tour player has a rhythm to their swing. In fact, the ratio of backswing to downswing are the same for all players even if they swing faster or slower. The book goes on to help you develop this same rhythm. It does this using music, counting, and a few other techniques.
It was really an interesting concept and the reasoning behind it isn’t very clear, but it worked for me. Some think the tour tempo shortens the swing, or promotes a smoother transition, or just gives people a more consistent swing though. In any case, it wasn’t hard to do and I downloaded some music to listen to before and during practice. It really helped. It gave me a consistent rhythm to think about during the swing and something to emulate while on the golf course. It made my swing more repeatable. It even improved my swing when I tried to give it a little extra. When I swung harder, I tried to keep the same rhythm, just faster. That helped, too.
All in all, it was a worthwhile exercise and it helped me break 80. Try it!