The problem with medlars is the size of the tree. There are no dwarfing rootstocks, or easy ways to train these to keep them small, so you will need a big garden to grow these. They will reach an eventual height of 9m (30ft).
If you decide to plant a medlar, then prepare the soil well in advance by digging in lots of well-rotted manure. They prefer well drained soil and try to find a spot where they will not be exposed to harsh easterly winds.
Buy your tree from a reputable nursery or mail order company. They will usually be supplied as a 3 or 4 year old standard or half standard, and plant between late autumn and early spring. Support the tree with a stake.
For the first 2 years cut back the leaders of the main framework by half each year, and then in the 3rd and 4th year cut them back by a quarter. Do this in winter.
Mature trees need very little or no pruning.
There are two common varieties available, Nottingham which has smaller fruit that are more richly flavoured and Dutch which has wider spreading branches and larger fruit.