That's why I like as-I-go debugging. When I'm coding, depending on how into a certain section I am, I'll constantly flip from my editor to the browser to run the script and see how things are going. That way I can catch problems before I've gone so far that I have to backtrace twice as long to find a typo.

My other favourite debugging practice is to flex my muskles, load a clip into the chamber, through on some gangsta rap, and starting sprinkling die() statements throughout my code. Then I can run it till it dies, see if it works, go to the next die... I've even found some notices pop up from time to time when I do that, that I would've never seen otherwise.

I don't know if this'll help any, and it's part of a script I did a while back so I haven't optimized it any time lately, but you can check out the image upload and thumbnail functions I use in my user authentication system here:
http://pastebin.com/m253910de
-m