I do UI design so I sam ure this won't apply but on the lotto-like chance that it might; I set up my work like an assembly line.

When doing HTML or MXML I concentrate on having all the art completed first including the wire frame or comp. Then I build the structure of the page, then work on presentation in CSS. I do not do HTML or CSS concurrently.

I think the key is to have a plan, make a procedure, then follow it. Don't bounce around.