If you put a little fairy liquid into children's paints before they start it makes it a lot easier to clean up. And it doesn't affect the paint at all.

I put a pvc/plastic table cloth on the table we use for painting/play dough/glue play. Just wipe it down when done.

Put newspaper down and something to cover up the kids,old clothes or apron that way when there done newspaper in the recycling or bin and what ever you covered them in the wash