If you ever hope to do significant amounts of writing, you'll need to manage your energy levels and mental focus over the course of a day's work.
You can easily do this by tweaking your eating habits.
On my most productive days, I start with a large, energy-dense breakfast, plus a couple of cups of strong coffee. This combination works perfectly: coffee gives me a good wake-up jolt, while the large meal gives me plenty of fuel to last the entire morning. Mornings are usually my period of peak productivity, so if I happen to have an especially good writing session, I can keep going for hours without interrupting my momentum to eat.
If my writing isn't going well, I'll usually take a break sometime in the mid-morning and go for a run, and then come back and take another stab at more writing.
Another key point: Breakfast is my only large meal during the day. Rather than eating a large lunch, I'll eat two or three small, quick meals over the course of the day. A typical meal might be a fruit smoothie, brown rice or some pasta.
Eating a few light meals like this keeps me from slipping into a food coma--a huge productivity killer--but it also keeps my blood sugar from getting too low, which can also sap my energy and my cognitive skills.
Readers: What dietary hacks do you use to optimize your writing and working over the course of a day?