There are two factors:
1. File Size
2. Dimension Size.
First step, resize the dimensions to 800x600, or 640 x 480
Then see what the file size is ( 250 kb or less is the desired size )
It all depends on what picture quality the camera you are using is set to originally. Mine is pretty high quality settings, so the file size is very large to start with..... so I resize mine to 640 x 480 right from the start.
Once you discover the best 'size' for your camera, you will be set.
Start with 800 x 600 and see what the 'file size' is in kb....