Almost the same as you do for a big one. If it's in a pot don't forget to water and feed it. You won't need to prune hard just take out any crossing branches and try to keep an open shape, (Best done in the winter) This stops branches rubbing and helps with air circulation. Mine's in a cottage garden border and fruits really well. I thin the apples out when they are still small as a large crop can become too heavy and snap the branch. I fork a little fish, blood and bone around the tree in the spring. Apart from removing any damaged apples from time to time. Just sit back and enjoy.