This sounds counterintuitive, but: learn when to take breaks and step away from problems. Some of my most productive hours have been spent walking through parks, coming to crucial realizations or designing approaches that end up saving me days (or even weeks!) of wasted effort.

Along the same lines, the best advice I ever received was from an old music teacher: do less, better.

Also: if you think "delegating" and "managing" are luxuries and somehow antithetical to creation, I'm guessing you haven't done much of either.