Air Conditioning - Best way to save energy?

I would like to know how to save energy while using the ac.

We have central air a/c.
Let's say that it's going to be a really hot day, my mom likes to wait until it gets very hot to turn on the a/c. I think that turning it in the morning when it's not as bad would be better, since it would hold the temperature, and not have to lower the house down 20 degrees like it would if you turned it on during the hottest day of the year.

What's the best highest but most comfortable temperature for a/c? I think 78 degrees is.

Would a programmable thermostat help save more money on cooling?

Thanks

I forgot to mention:
We also have a ceiling fan in each room.
It's a 2,200 square foot home

Let it run 24/7. Thats so it get the humidity out of the home. Then you will feel cool at 78o. Thats like if it gets cool out and you open up the home BAD bad. It takes like 5 days for the AC to get the humidity out of the home and dry again.

Thanks :)

My mom likes to turn off the ac and open the windows, but I'll have to show her this.

Temperature and humidity within the home should be maintained at a near constant. Temp around 70 and humidity 35-55%. Opening up the windows and dumping in allergen laden air and high humidity is not good for solid hardwood furnishings or allergy sufferers. It is best to simply keep the thermostat set at a constant.

If cost is an issue, which is to me as I am very frugal, I keep my AC thermostat set at 78 degrees and run a little fan in my bedroom. In winter, depending on how brave I am and how much I can afford, I keep it set low. Last winter I splurged and kept it at 65. The winter before at 55. Last winter I had a computer and was here on the website at night. The previous winter I came home from work and got into bed under the covers because I had no computer.

To conserve in warm months, keep AC at 78 degrees and run fans. Keep windows closed to keep out humidity. Warm, humid air will harm furnishings and make you feel warmer. In winter, be conservative, layer up, reverse direction on fans to direct warm air down toward floor, and lower thermostat setting. In warm months, reverse direction of fans to move warm air toward ceiling.

If you are comfortable at 78 then set it at 78 and leave it.

Mom gets a point in airing out the house. Assuming you are not allergy sufferers, when you get a cool day with low humidity open the windows and let nature cool and air out the house.

Remember that your a/c is recirculating the air in the home, an air change may be good every once and a while.

Twelve told you how he keeps his house, keep yours how you want it.

Mom looses a point for waiting to turn on the a/c because it takes longer and costs more to cool from (say) 85 to 78, than to just keep it at 78.

And as Twelve said use the fans. Keeps air moving and evens out the whole house temp.

Thanks all!
You have very good advice! :)