Posted By North Star.
To keep a paint tray like new, insert it inside a plastic bag. Pour the paint into the try. When you're finished painting, pour the remaining paint back into the bucket (or an old jar if there's just a little bit left.
Glue a paper plate to the bottom of the paint can. The plate should be an inch or two wider all around than the can so it can catch drips. This saves you the trouble of moving newspapers around under the can.
When using an oil-based paint, keep a bottle of nail polish remover handy. Clean up spatters by dabbing with remover on a cotton ball.