you don't have to think : "oh what should i paint?" that it's a bit stupid that magnificent idea will came by it self don'i push it or if you want to paint just sit down and do it, sometimes when you don't think about what are u doing in the end your work can be great great for one thing that the work will be came from inside u know what i'm saying?
ya I gotta agree with the above posters, just let the ideas flow, don't force them. however, I do alot of forcing, so I'll throw my 2 cents in. Usually I try and think of the balance ahead of time if I can't think of an overall idea. Place wherever you feel (and honestly doesn't matter) should be the center of attention in the painting. After that, draw a circle in that spot.... now stare at that circle. Something'll hit ya eventually.
I think I know What I'm gonna paint, a brigth orange sky with fluogreen ground and a purple tree with rainbow colored leafes. I had a dream about it
What I usually do to be inspired is I would look at the paintings of my favourite painter and his/her contemporary. That usually gives me some inspirations.
Pick a colour.... cover one of your hands in it... pick another and have a pot of it next to you... spread the paint covered hand across the page... then with the other hand take the new colour and add ... pick more colours... add glitter... and ribbons..... and then see where else it takes you... i did that and crated a wonderful collage on canvas ...paint with your hands.. nothing is more satisfying than beiong covered in paint