My favorite way to do this is with Picasa. [removed unofficial link and replaced with Google's official link] which is also free. After doing whatever editing I need to do I export the photo to a new album, and when you click the EXPORT button you're given several choices in what quality & size (in pixels) you want as the largest width or height. For Quality you get the choices of Maximum, automatic, regular & minimum (or something along those lines) PLUS Custom. If you choose custom you get a slider to set from a very low value to a max value of 85%. Because every file is a bit different in it's original file size which changes when edited & or cropped you'll need to try saving at a few different custom settings to learn what fits your needs, but none of that takes more than a few minutes.
"A skill is developed through constant practice with a passion to improve, not bought."
