I've found that with certain programs like Lightroom, there is an option to export as a certain size, you can select "long edge" and "850 pixels" and this being the max size APUG will allow of 850 pixels usually makes a nice crisp image, I don't change the exported amount of detail, I keep the export at 300dpi but don't put size limitations on the file install (like requiring the file to be no more than 100k) but let it do it's thing... If I limit the size, my images aren't as crisp.
Hope that helps.
EDIT: Also, if I DON'T define the "long edge" pixel count, and the size is larger than 850 pixels, then when APUG re-sizes the image, often the colors and tones are off, I know Sean has said their server SHOULDN'T affect the image colors, but in my experience it does, so make sure you creat a size under the 850 limit or you may run into issues with the "look" of your image not matching the original on the computer.
Mamiya: 7 II, RZ67 Pro II / Canon: 1V, AE-1, 5DmkII / Kodak: No 1 Pocket Autographic, No 1A Pocket Autographic | Sent w/ iPhone using Tapatalk