Killer Poker Online by John Vorhous helped me vastly with my cash game. Not necessarily regarding specific hand strategy, but more on approach and discipline, attributes that players often already consider themselves to have no problem with.
I've just bought that one Snoppy, finding him a bit condescending in the initial chapters so struggling to keep going with it. You think it's worth sticking with?
Yes. And take note of what he says. He may appear condescending, but he doesn't mince his words and eventually you start to realise that a lot of what he says is spot on. You'll start to tell yourself, 'Good Lord, I do that.' and 'Yeah, that's true.' Sometimes it takes some1 to be brutally honest to you be4 you are able to accept that there are flaws in your game.
Everyone's different, but it worked wonders for me. He told me to get a grip of myself, and I finally listened.