Find something the child loves and use that to inspire him or her. For example, I once had a student who wasn't keen on writing assignments, but once I let him incorporate football into assignments, he begin to enjoy it.
For things like math - turn a skill with which they need practice into a game. This almost always works.
A third thing that works well with my particular children is to make up songs (or use already available songs) to help them learn what they need to learn. Skip counting songs, for example, or songs to learn the presidents or the states and capitals.