Much has been written about patterns. I'll share two things that helped me get into the upper registers:
1. Try to clear out balls from underneath rack early. I know the conventional wisdom is to clear balls off the rail first, but I find the game to be easier when your final pattern is picking off balls above the third diamond by the foot rail, even if it involves balls on the rail. Balls on the rail can be great key balls.
2. Try to look for patterns that don't involve the key ball in the side pocket. If there's a fool proof way of getting there, go for it. But I've botched a few runs being dead set on that set up when in hindsight I should've picked a simpler pattern.
Take a look at Mike Sigel's consummate run here and I think you see these two points in action. While he played the side pocket key ball pattern a few racks, he played some beautiful patterns without them. Notice the rack with the side pocket break shot. Many players - myself included! - probably would've tried for a side of the rack break shot with a side pocket key ball. Mike chose the simplest route.