We haven't had a bona fide heatwave here in Texas, at least yet. We've had 100 degree days as usual, but last week it rained nearly all week. Some days pretty hard.
What I do to keep the electric bill low is I never use the oven during July or August. I use those two months to clean it, a little at a time. I don't like using the 'self cleaning' cycle. I prefer the level of clean when I get my own self to clean it :)
Also, I live in a state where electricity has been deregulated, for over a decade now. It pays to shop the rate. With no changes to the HVAC unit, no changes to how often we're home or how the thermostat is programmed, the bill has gone down 60.-80. dollars just from changing electric providers.
Keeping up with the exterior caulk is another one, especially on the side of the house that gets the full afternoon sun.