Depends- what are you photographing indoor?

If you want your lights to look like many pointed stars, use F22 If you want them to be almost star-like, use F8-11

If you are just photographing one object indoors and want your background to be out of focus and the object in focus, use F 2.8

Very important- use a tripod for any indoor shots, you don't want high ISO grainy discolored pictures or blurry pictures because your hand is shaking. Let the camera auto-adjust the shutter speed for you, if its too dark/bright- then adjust it manually depending on how dark your indoor room is.

Play around with white balance when you take the picture- it'll make your photos' colors more blue or red, or use photoshop to adjust your colors after the shoot. For good photoshop adjustments take your pictures in highest format- .RAW for canon for example

I'd recommend shooting in RAW, including a calibration shot of a grey card (or clean white paper if you've not got a grey card to hand), and use the to post process.

There are times when you need the benefits of shooting in JPEG (for example, if you wanted to record the action at an indoor tennis match), and here you can use the custom white balance option of the 5D. From what I remember of the procedure for setting this up on a 20D, you essentially take a photo of a neutral scene (i.e. a grey card) in a calibration mode, and the camera calculates the colour temperature from this -- full details should be in the manual that came with your camera.