My biggest piece of creativity advice for writers & illustrators (all ages): make time to PLAY.
No matter how busy I am, I always try to carve out a few minutes every day to do some art and writing purely for the fun of it. No pressure to show anyone or have anything be perfect....just to PLAY.
I find if I don't make regular time to just play and experiment, then I slip into a rut, not pushing myself to try the new and different, and I also start losing the joy.
DON'T LOSE THE JOY.
Make time to play.