Before choosing an air conditioner there are several things that you may need to take into consideration. These include

Location:

Where you live will considerably affect the operation of your air-conditioner. If you live in an extremely hot climate be careful to ensure that the unit is designed operate in high ambient temperatures. The same applies for people living in cooler climates. The outdoor unit must be designed to operate in low or minus zero temperatures. Not all units will do this.

Orientation:

If the room that you are trying to air-conditioned faces the North it will require more energy to cool a room down. On the other hand if it  faces south it will need less energy. The opposite will apply if you are trying to warm the room.

External shading:

Objects providing shade such as blinds and canopies, as well as things like trees and shrubs can considerably cut down the amount of heat entering a room.

Internal shading:

Although things such as curtains and blinds are not as effective at keeping out heat as external shading, they can still have an effect.

Insulation:

By insulating your roof, walls and floor you help to regulate the temperatures within your house. This also significantly reduces the load on your air conditioner.

Sealing:

Take the time to minimise gaps around windows and doors etc which will reduce the unwanted hot or cold air coming into your home.