Lots of reading, I always seem to be reading!
When I'm having an 'off' day, that is to say a day when my brain resolutely refuses to obey the simplest of commands, the only thing I can do that is 'creative' is to read a book. It must be art-related; but it can be from the library or my own collection. It will usually have links to at least one project in my 'to do' list. Sometimes though it is nice to read an art book just for the sake of learning something new; or learning about art from the perspective of another artist. You don't learn about art just from your own drawings and paintings. You also learn from others, especially when they describe the pitfalls to art. Sometimes I look at an artists' work and think, 'wow, I am definitely in the right job', because I can see their work in print and think 'I know that I can do THAT!' :o) You need to see these books sometimes because it is good to know how far you have come an artist yourself. Yeah, I know, maybe it makes me sound like a right big-head but hey, if you think you can do something to the same level as someone who is already in print, then that's a good thing right? It means that some day you might get to be in print too... and then you will be picked apart by the next bright spark that comes along! What goes around comes around I guess! :o)