Insulate the hot water pipes you can reach
Added
Measure the exposed pipes at your water heater, under sinks, and in a crawlspace or unfinished basement, then fit foam or fiberglass pipe sleeves and tape the seams. It's a low-skill DIY job; wear gloves, long sleeves and a mask if you handle uncovered fiberglass.
The result
Result: DOE/PNNL Building America guide: insulated hot water pipes deliver hot water faster, cut heat loss and water-heating costs, reduce wear on the water heater, and help protect pipes from freezing.
Note: Use protective gear with fiberglass, and keep insulation clear of the water heater's flue and burner area.
Source
DOE Building America Solution Center (PNNL): Insulate Hot Water Pipes (opens the original source in a new tab). Check it for the latest numbers before you act.