Service your air conditioner is just a waste of money
No never. Every gadget requires a proper upkeep too have a reasonably long lifespan, so is an air conditioner. A professional tune-up will lead to thorough clean-up of the unit. It will detect small snags that have developed over the years and resolve them before they blow out of proportion. Avoiding maintenance of A/c will only generate costly repair bills often.
To save money you should turn off your air conditioner or set the thermostat very high.
When you come back and turn your cooler, the A/c will work harder and longer to cool the house. Turning a lower temperature will not cool the room faster. A/c units only run at one speed, so a lower setting simply forces the machine to run longer. In fact you can use programmable thermostat that will run the A/c at moderate levels the whole day when you are out. It starts cooling, say an hour before you get home.
Buying a bigger unit will produce better cooling
This is a hoax. It is a trick often used by HVAC contractors to persuade you into buying a bigger unit which will of course be expensive. A bigger unit will cycle to frequently which will not cool the room effectively. An A/c besides cooling also dehumidifies the house. Frequent cycling will disable the unit from purging the moisture from the room air effectively. Your room will feel clammy and uncomfortable. Also do not buy an undersized unit; it will work hard to keep your room cool. It will hardly cycle off, and over-dry your air. Buy an energy efficient and properly sized AC unit to get the best possible comfort.