I really enjoyed Randy Susan Meyers' recent post on "Photoshop-Botox for Author Photos." An additional thought, based on my days at a magazine where I was in charge of photo-editing: Be careful of poses that are difficult to crop. Bringing your knee or your hand up by your head may look really cute when we can see the full-body posture. But if I've got a box in layout big enough for only your face, a random knee floating by your left ear--or an index finger thoughtfully crossing your chin--is going to look mighty strange.
Every author photo is really four photos: the color version, the grayscale version, and for each of these, a "big" and "small" version--a print-ready file of 300 dpi, minimum 4x6 inches, as well as a web-friendly version at 72 dpi, minimum 2x3 inches. Why multiple file sizes? Traditional printing processes require a lot more "dots per inch" of ink in order to define an image, whereas our eye registers a picture on screen using much less data. Those who work online don't want to have to upload hefty files that clutter their server space; printers forced to run less than 300 dpi end up with grainy or blurred images. JPG is the current standard format (a few publications request TIF, but can usually deal with JPG in a pinch). BMPs from Paintbrush are not acceptable, nor are GIFs--it's a function of file size, compression, and palette management.
Name your file "[Last name][First name]" (i.e., "DoeJane") or, if a credit is needed, "[Last name][First initial]Credit[Photographer First name][Photographer last Name]" (i.e., DoeJCreditMattBell"). I can't tell you how many author photos go to magazines having just been ripped from a digital camera--with the nondescript, overly long file name to boot. If a file like that gets saved to a folder, it's really tough to find again. And in the last-minute stages of proofing, it's really handy to have the author name (and photographer credit) embedded for reference.
You can read the whole post here.