Black text on a white ground is the easiest to read.

Set background, text and links in contrast (most users expect links to be blue).

Match the background to the tone of any background image to aid anti-aliasing.

The commonest form of colour blindness is red/green so make sure you have strong contrast in the blue element and in overall brightness.

Check in all available colour depths, greyscale, monochrome and a cheap LCD screen.

Check usability with your grandparents

Try to keep things as simple and easy to use as possible.