So you have your heart set on buying an above ground swimming pool, after all they are very cheap compared to an in-ground pool, and if you move house you can take the above ground swimming pool with you.
Also if you put it up and then decide it is in the wrong place you can simply move it. This brings me on to the subject of preparing to install an in ground pool.
Whilst it is very easy to go out and buy a small 15ft circular above ground pool, you still have to bear in mind that when full, it will be holding several tons of water, and if the side panels were to break the resulting onrush of water could cause a lot of damage to property as well as anyone in the way.
You need to prepare a flat and level surface. Your garden may be on a slope that is perfectly flat but it is still a slope and not level. Building an above ground pool in such a location would cause the water pressure to be uneven against the sides of the pool and would result in catastrophic failure.
You also need to think about providing adequate drainage for when you have to empty your above ground swimming pool. This is a serious consideration as a large oval pool could hold over fifty tons of water!
You need to lay down sand for the base of the above ground swimming pool to sit on in order to take out any imperfections in the ground, after you have removed the turf.