What are some tips for shooting green/blue screen footage?
Jonas Hummelstrand has a great guide over on his blog - General Specialist that details out a bunch of tips for it (including descriptions and pictures), I'd recommend checking that out.

Ultimately the #1 key is lighting - you have to maintain a smooth and consistent lighting job on the backdrop so that the camera "sees" a consistent blue/green free from dark and light spots.  Not only does this make it easier to remove the background, but it means you can use a smaller "slice" of the color spectrum and thereby makes it less likely that you'll accidentally remove part of your foreground subject.

The #2 key is separating your foreground subject from the background (once again, to make the edge definition clear and easy to define).  You want to put at least a few feet between them and the screen (to reduce the amount of green/blue light reflected off the wall and onto them).  If you're using a greenscreen, it often helps to use an amber backlight for your subject (being the opposite of green means that amber cancels any bounced off green light).