how do i care for a christmas cactus without making a mess?

Most of them are killed by overwatering. Water when the top inch or so of soil is dry, then let it drain, never leave it sitting in a saucer of water. Hard water is fine for them. To get flowers, it needs cool nights and long dark nights in autumn - a spare room with the light off in the evenings works. Once buds form, don't move it around, it drops them if you do.