Reposting this from CG Talk in 2005. Super Helpful, thank you _mg_
This is a simple way to have a camera always track the character you’re editing.
It allows you to move/rotate the cam relative to the /character object so can always adjust your view but will always follow the character.
1. Create a target camera.
2. Create a null and align it’s position to the Characters root bone/effector.
3. Move the camera so that it’s looking approximately at the characters root as in a mid-shot of a character.
4. Ensure that the camera target is a reasonable distance from the camera body, but not too far.
5. Parent the camera and target to the null.
6. Position Constrain the null to the root node.
7. Play your scene.
You should now have a camera that always follows the character, but still allows you to orbit or zoom around the character.
Hope you find this useful.