Here are some tips & tricks that are very important for a graphic designer who's using Adobe Photoshop. Soon, there will be more.
Making TV Scanlines in Photoshop (TV scanline effect can be used for different purposes, mostly for stylistic enhancement. Here's a simple way to create TV scanline effect.)
Transparent GIFs in Photoshop (This is a very simple way of achieving transparency for GIF images for Web pages.)
Layer Mask ( Layer masks are fairly easy to use, but a little mysterious. They can, however, produce some pretty spectacular results and are worth playing around with. )