1. All craft projects are primarily done on some plastic serving trays I got on clearance at Target. This gives us a place (with a rim in case of spills) that she can be messy, but almost everything wipes off. Even dried-on "permanent" paint comes off with a bit of persuasion. And when we need the table for a meal, we can pick up the whole craft and move it out of the way.
2. I've been using heavy-duty foam plates as palettes for the paint, which lets her mix the colors together but limits the volume of paint she gets at any one time. The foam plates are easy to wash off and reuse over and over ... I just finally got rid of the set we'd been using for the past two years. Now we're using some disposable plastic drink cups. I cut the tops off of them so that each cup is only about 2 1/2 inches deep. This means that they're low enough to be hard to tip over, and again, it limits the amount of paint the kid can have. They're also low enough that LazyKid doesn't try to rest the paintbrush in them, which means she doesn't catch the paintbrush with her elbow and tip them over that way. These are wash-and-reuse items, too. We've also used styrofoam egg cartons as palettes, but that's harder to share among several artists, since all of the cups are stuck together.
3. Lots of paper towels, right there at the scene. It's much easier to clean up a spill if you don't have to run across the room to get a towel. Plus, if the towels are right at hand, it's much more likely that LazyKid will try to clean up the mess herself before asking me for help. We've also had good luck with using up some old packages of baby wipes as craft cleanup wipes.
4. Storage for the paints that makes them easy to carry without dropping or spilling. We've only got a few acrylic paints right now, so they're in a small shoebox that's stored with the rest of the painting supplies in a plastic tote. The plastic tote has all the poster paints, paint brushes, paint stamps, palettes, and stencils, all in one place. When we want to paint anywhere - on the easel in the basement, on the floor in the livingroom, at the dining room table, outside on the picnic table - we can just grab the tote and take everything with us in one trip.
5. Lots of supervision. If I'm not actually doing the craft with her (I helped paint some of the larger diorama figures above), I try to be physically with her at the table while I do something crafty on my own. I've got a number of mindless knitting and crochet projects I can grab to fill in a few minutes while LazyKid paints or works with clay ... things that can be picked up and put down a lot without getting messed up too much. I've found that trying to do things away from the table - like cook dinner or wash dishes - ends up with the kid making more of a mess than if I'm right there.
Hope some of these tips help keep you (and your table) crafty but organized!