ForTheLose.org has 11 tips that will help theme designers speed up their theme creation process. For example:

Tip #5 – Copy & Paste Old Theme Files

I figure this tip is common sense, but you never know. Once you’re done with the static files, it’s time to actually get to work in Wordpress. Crack open your text editor of choice and get to work creating all of the default Wordpress files. I recommend starting from archives.php and going up in alphabetical order. Go ahead, I’ll wait.

A lot of the tips are about not reinventing the wheel, and keeping focused, so it’s also about attitude aside from knowing the ins and outs of WordPress theme development.