Although mushrooms may be found in many and varied places, there are two main type of habitat that most mushroom hunters focus on. These are: pasture and woodland.
Pasture basically means grassy areas. However, some types of grassland are better than others. The best are fields that are used for year-round grazing of animals (farm or wild). The animals keep the grass short which the fungi prefer as well as fertilising the land. Natural heath land is also a good option. Land which is used to grow hay is not so productive (for fungi) because of the long grass and the disturbance caused by heavy machinery.
I’ll pass on a useful tip here - Google Earth. You can see mushrooms from space, honest! Well, not the mushrooms themselves, but the tell-tale rings that some species (such as Fairy-ring Champignons) leave in the grass. These rings are clearly visible on satellite images, so you can select likely fields to visit whilst sitting at your computer (just don’t tell your boss that I suggested it). Satellite images can also tell you whether a patch of woodland on a map is coniferous or deciduous. This is useful if you're searching for species that grow with particular trees.
Many fungi, indeed the majority of edible species, prefer woodland. This may be a small copse or the middle of a forest. Some of the woodland fungi grow on the decaying leaf litter on the woodland floor, while others have a direct relationship with the trees they grow under. Many species of fungi only grow in association with certain types of tree. Consequently, woods in which favoured species of tree predominate are likely to be more productive. Trees which are good for mushroom hunting include: Beech, Oak, Birch, Pine. Woods that are predominately Sycamore or Elder are likely to be less productive.