The only, and I mean ONLY, way to increase your hiding is through macroing. Otherwise you'll go insane. Just put the hiding action on your hotbar, and set up a macro that spams that hotbar key constantly. It gains on use of the skill, but it gains so incredibly slowly that you cannot hope to even get a single point by yourself. Even if you just hit the button constantly while playing you probably won't get a single point of it. Just macro it overnight... and even then, you'll probably only get like 5-10 points in 10 hours depending on your current skill. It's pretty much the biggest grind in the game right now.