The single most important thing you can do as the operator of a heating or air conditioning system is to change the filters every month. An air conditioner or heat pump needs to breathe! Your furnace or air handler is trying to distribute heating or cooling that you have bought and paid for already and you can help. There is no use in buying High Efficiency heating or cooling if you won't do your part. The useful life of a filter is about a month at my house, so I check the filter every time I pay the rent. I use the 40% efficient type that say every three months is often enough but I know that every month is better in every case and essential if you have pet's, Frequent dusting and vacuuming also stirs things up so in effect the cleaner you keep the house the more airborne particulates end up in the filter. If that sounds a little stiff then please understand I really don't want to pull out your filter (and charge a house call) and find it plugged solid. It's also a little embarrassing to my customer, and makes me wish I wasn't witness to it. So change the filter regularly friends. Or at least before I come to visit.

Along those lines, please do adjust the register levers to get a good air balance from room to room, just check that when you are done not more than about 20% are shut off all together. This will also cut efficiency and overheat heating or air conditioning components throughout the system, motors mostly. 
 You can get the best balance of your duct system by adjusting the dampers at each branch duct right where it heaves the main duct, or main distribution box. You'll have to poke around under the insulation a bit to find the handles. 
 In line with the round ducting as it leaves the main duct (parallel to) is wide open. Across the branch or leaving duct  (perpendicular to) is shut off. but don't worry these things are not air tight so closed ducts are not really all the way closed. So, why freeze in that little guest bath when adjusting one handle will fix it. This is a great way to get extra air in the bonus room that never seems to get enough cooling.

Now about outdoor airflow. Keep the bushes cut away from the condensing unit, even if they're beautiful. A heat pump runs year around and is usually okay in winter, an a/c unit is subject to overgrown landscaping which will cut the efficiency and increase operating cost, while it's shortening equipment life. If you turn off your airconditioner while you cut grass, or at least cut away from the A/C or HP unit it will run cheaper!

I despise Holly Bushes and every time I get stuck I think about raising prices, (not really)  but I would, give a free coil cleaning to anyone who says they cut one down if it was growing near my air conditioner!

Further care for your condensing unit, (AC or H.P.). It would like to have a free airflow straight up for at least 8 feet. No overhanging branches, new decks, no roofs or awnings of any kind. This part of your heating and cooling system rejects heat from inside the house and its own motor heat as well. The harder it works the higher the pressures and the electric bill in almost direct proportion follows head pressure.

One more note to save you a quick $ 125.00. Just because I like you! Ant's love electricity or they are suicidal ( I am not a "bug psychologist" ) however, I know they will crawl into the electrical compartment of your air conditioner or heat pump and commit harakiri on your compressor start relay. It's no use cleaning them out and trying to reuse the relay, it will only stick again and may cause compressor problems. Keep the ants away with chemicals or whatever means seems right to you (WD-40) and it will save you a breakdown and 125.00 plus house call. If you plan to look inside turn off the power outside, never mind the buzzing it's low voltage and will probably not kill you. Be safe cut it off at the furnace or air handler and at the condensing unit. I replace a dozen failed contactors a summer, during "ant time" which fades as summer moves ahead.

Finally on airflow: You can inspect the heating cooling ducts yourself and since they are mostly cheap plastic now you can repair any air leaks with duct tape (be generous) and save money while you increase comfort. Increasing comfort is my goal in the trade and in life ( how Zen of me) and duct tape is the solution. It sticks to itself best so give it a good wrap. Why air condition the spiders? 
 Besides, you will be in the minority of people who have used duct tape to actually repair a duct!

There is more to say about air but let's move along.