If you find a really good soil, then apart from adding manure, compost, seaweed meal and sometimes wood ash each year, you shouldn't need to do much to build up a useable soil, constantly replenished.
There are lots of gardening and agriculture books which tell you how to assess a soil. For example you want to see if it's sandy, clay, loam, or in our case volcanic (from a very long time ago I'm delighted to say
). best wet to check this - rub some between your fingers to see how gritty or slick it is, squeeze a handful and see if it claggs together or doesn't stick at all - or midway, which is ideal for most purposes. Estimate the humus content by feel and by the darkness. There are ways of doing this involving jars of water and letting the layers separate out, but a bit difficult to do in the field.
What you are looking for is if the soil is heavy clay, which will be impossible to work when wet, slow to warm up in spring and forms a surface pan easily. Clay is very fertile though. If you have a sandy soil then although it will be workable all year round, and warms up quickly, it is so free draining that nutrients are washed out quickly, taking any fertility with them, and it doesn't provide for much root stability. The ideal is somewhere in the middle.
The surrounding natural and farmed vegetation can tell you something about the soil. Certain species of plant like sandy soils, dry soils, wet soils, acid soils, rich soils and so on. Look at what there is growing and work out from there an idea of what you will be able to grow.
Time I went and did some work in my own soil........