I truly enjoy the L drill, it's somehow just out of my reach to finish it.
I'd illustrate it but I'm sure y'all have seen it. Make an L out of all the balls, half of them in a line from the head spot to the short rail and the the other half from the head spot to either long rail. Shoot the shot nearest the short rail first and just continue along the line. Each time the cue ball should hit 1 rail, or maybe 2 depending. If you have to play it some other way, it's ok, but don't bump into any other balls.
It's harder than it looks and I'm always feeling pressed to try harder to complete it. It's tough enough that you won't just jump up and do it and then repeat it or move on. You're gonna want to try it over and over until you at least get one arm of the L.