Summers here in Virginia can get pretty hot... triple digits many times with high humidity in July and August. Those are the days that I hide inside with my fair and freckling skin. Though we need to replace our heat pump this summer (someone console me... it will cost thousands of dollars), I do have some energy saving tips to share with you on how we keep our home cool, plus a few others I've learned along the way that don't apply to our situation.
Doors and windows: Keep them shut. I realize this is a "no brainer", but our kids are notorious for not bothering to shut the door on their way outside to summer fun. Stress to the kids how much energy you lose out the door and even resurrect those infamous things your parents said to you, namely, "I'm not paying to heat/cool the outside!" Air loss = cool air that isn't staying inside to keep you comfortable.
Shades drawn: This is a must for us, particularly with our back sliding door. If the blinds aren't drawn, the sunlight comes inside and heats up the kitchen area. Plus, I have some neighbors that look in... do I really want them watching me?
Thermostat: With winter gone and spring nearly past, it's important to readjust your temperature needs. In the winter, you seek warmth. Perhaps it is the snow outside making you perceive that 75 degrees is pretty darn toasty. That same 75 degrees feels too hot in the summer. (Or maybe that's just me...) If 75 is your perfect temp now, try to acclimate yourself to not mind an extra degree or two. If you work away from the home all day, having the temp up a little bit during the hours you aren't there won't be noticed. Many thermostats can be swapped out for ones that allow you more control over when the air kicks on, including the ability to set temps for specific time periods.
Service your heat pump/AC: Don't wait for it to break. The air conditioner man will come, though you'll likely be in a long line of people who called him during the heat wave who have had their units go down. Get a check up for your unit before the massive heat rolls in. Something I did not know was how a heat pump worked. When an air conditioner installer explained how the system worked (in reverse to heat in winter), I understood why my bills were high if I was low in coolant during winter months (when you don't necessarily notice anything is amiss, other than the sky high electric bill...) If your unit is old, prepare to cry because they may not make your refrigerant anymore/parts for your unit anymore and the cost to replace is a bit staggering to say the least.
Learn to love your grill: If your house is small or, like mine, has a very open floor plan, turning on that oven for a few hours to cook that roast means the whole house heats up. To combat the heat and to help our AC unit not tax itself so much, we try to use our grill whenever possible. It's hot outside - so let the heat from cooking go outside too. Another tip: don't use the self-clean function of your oven in the summer. Ever.
Keep your filters clean: Dirty filters means your unit works harder. Aim to change your filters once a month, but only use filters that are rated for your unit. We once changed to a filter that would trap more pet hair; however, the air conditioner repairman let us know that our unit worked more efficiently with a cheap, fiberglass filter and that we were taxing our system using a filter that it didn't have the power to draw air through as well.
Can't afford your bill: Check with your utility company as they may have a program for you. Often, you think about assistance with heat during the winter. Folks in the summer have nearly the same needs because of the need for air conditioning during the brutal heat waves too. If you have trouble affording your bill, definitely make a call to see if there is any assistance that they can provide you.
Foundation Vents: I was always told that these needed to be open in the summer and closed in the winter. Their use is to help control humidity in your crawl space so that your wood doesn't rot/get moldy or become a beacon for termites. I am not such that much air flow goes through in the summer though. However, I definitely close them in the winter because I can tell a difference in the temperature of my floor when they are open versus being closed. The floor is much less cold with the vents closed in the winter.
Weedwhack carefully around unit: With our outside unit, we need to be very careful with weedwacking. There is a line that goes out and it is supposed to stay covered with a foam insulation sleeve. When the sleeve was absent, the line actually froze, causing us to have to shut it down for many hours. Trim carefully around your air conditioner's outside unit to ensure this doesn't happen to you. Remember, any extra work your unit has to do to keep you cool is lost savings by way of a higher utility bill.