1
Make sure that the shells you buy are at least slightly larger than the shell your hermit crab currently inhabits. This will ensure that the crab can fit into its new shell as it grows larger.
2
Choose what type of design you want to put on your shell. Flags colors, stars, or any kind of design will do. While choosing how you want to paint your shell, remember that hermit crabs like shells that are brightly colored. Also remember that a dark shell could be very hot for the hermit crab if he's already in a humid habitat.
3
Decide which parts of the shell you're going to paint which colors. You don't want to make a lot of mistakes while painting the shell. If you make a mistake that you really don't want to deal with, you'll have to wait until the shell dries to fix it.
4
Paint the shell using the acrylic paints and design you chose. Do not get any of the paint on the inside of the shell. Apply the small (very small and light) objects you chose if you wanted to add a bit more decoration. After completing this step, allow the shell to dry for at least 24 hours.
5
Place the shells into your hermit crab tank after they have fully dried. Do not be frustrated if your crab doesn't go directly into your shell. It may wait until it molts, or it may just wait until night time (hermit crabs are nocturnal).