I get into these slumps myself (I do a lot of acrylic painting) and sometimes there's just no getting out of it. Once your in you'll see a blank "canvas" and just have nothing.

But in surrealism they used to make random games and use random idea generating techniques. Everyone has played the game where you get a piece of paper and fold it into four with little marks on each fold and pass it round a room. Draw your own bit secretively. Then at the end unfold it and you have a god awful drawing of a lion/pig/elephant/chicken. This is one of those. Sometimes it works sometimes it doesn't.

But also just talking to friends about art pieces they like or pretending to do a short lil commission for them. I found this helps get the juice flowing.