My first tip that I have of something that works for me is:
Using empty egg cartons as paint holders. When Graycen finger paints we use the Crayola Washable Finger Paints - which by the way are wonderful!! They come in a squeeze tube and are a gel like consistency. Graycen doesn't always want the paint just dropped on the paper, so what I have started doing is cutting the cups from the egg cartons in twos and using those as her paint cups. I squeeze some paint in them and she dips her little fingers in and wipes it all over the paper. When she is done painting, we toss the cups! One less dish to wash and it's another way to reuse something that you would have tossed in the trash in the first place!