Okay here is a tip you can use and not "Tape plastic over your windows to seal in the heat" which is ridiculous. Who does that?
Call you power company and tell them you would like to get set up on their budget billing. In our are what this means is that instead of getting surprised every month when you get your power bill you have a set amount each month that you pay based on your last six months worth of use. So whatever the average is for that six months, that becomes your flat rate that you pay.
I did this recently and it was awesome! We had bills from $97.00 in the months where we did not use heat or air conditioning to $278.00 in the dead of winter for a 2800 square foot house. Our monthly fixed payment is $135.00. What?? Yes, $135.00 per month. Every month. Now this is not a license to freak out and use all the electricity that you want to because you have the same monthly payment each month. They regulate it by doing an audit on your power usage every six months and reconfigure your payment to that. So as long as you don't go crazy and use relatively the same amount that you have been using then your payment should stay around the same amount. Ideally you will be practicing all kinds of power saving strategies so your bill would actually turn out to be less when you came up for audit.
The second blessing in this is that you now can budget exactly what your power bill will be each month - no more surprises.