Here's an easy thing you can do to keep your air conditioner running as efficiently as possible: Don't crowd the condensing unit, the outdoor part of your AC. In the photo below, you see a common problem.
As the shrubbery gets bigger, it's going to crowd that condensing unit. When it does, it's going to restrict the air flow across the condensing coil. Basically, the condensing coil is where all the heatthat got picked up from your home gets dumped outside. Your AC is engineered to remove the heat by having a designed amount of air flow over the condensing coil. If less air flows over the coil, less heat is removed. That means the whole cycle warms up a bit, and your AC works harder to keep your home cool.
You'll pay extra for it in more than one way: (1) Your monthly electric bill will be higher; (2) your equipment may not last as long, so you'll pay more in repair bills and in having to replace the AC sooner.
Remember, keep some space around your condenser and let your air conditioner breathe!