I am not a Photoshop-adept by any means. I enviously eyeball people who effortlessly skate through layers, click frolickly on a filter here and an alpha channel there.... I can't stand it... I desperately want to be proficient at Photoshop but the reality is: I use it too little to ever really crack that nut.
For people like me, Video University has a helpful sheet with Photoshop for Video Tips & Tricks.
Some of the topics include:
Creating an Image for Video Use
Tips for Viewing Pixel Aspect Ratios
Extracting Elements from an Image
If you want to go more in-depth, Photoshop guru Richard Harrington's Photoshop for Video has gotten some great reviews on Amazon- and beyond.