no real magic, make the image as you would normally (with the right settings per protection etc etc..), cancel it at 1-2%, when asked if you want to delete the image say no.. job done, thats more or less it.. mostly trial and error in getting the right %age to stop at, its been discussed in other threads
you can also then go totally crazy on it to make it compress better by hexediting the image and filling the file data (yep the data the files would normally contain...) with zeros or a repetetive byte (you have 255 to choose from) which makes the image compress better, all a matter of personal choice though but only attempt the crazy things after you have tested the 'mini' image you have made works...