Av setting for aperture priority, make sure that macro is not on for full length pen shots. Set aperture at about f11 (effectively the same as f22 or so on a DSLR due to chip size) and set white balance manually to correct for your lighting. IIRC you can set a manual white balance on the S3IS.
Make sure that you are on the largest file size and best quality that the camera will offer. Use the timer to release the shutter so as to not induce camera shake from pressing the shutter yourself.
Use a tripod, and practice.

Cheers,
Sean