Assuming that this has been cleared of most rubbish, vegetation, etc., by the builders, the main aim at this stage is to get the ground worked into a state ready to take new plants in due course. Take your time. What you do now will affect the performance of everything you grow in the future, so it must be done right.
First, go over the ground and remove any remaining rubble and rubbish. Rubble which might be useful as hardcore could be stacked in a heap and used later as a foundation for paths or similar, the rest disposed of.
Now, consider the time of year, and the weather. If it is very frosty, snowy, or wet, walking on or messing about with the ground can only do more harm than good. If you are in the middle of a sweltering drought, you probably will not be able to get a spade into the rock-hard, sun-baked surface, and even if you can, it is likely to do you more harm than good.
Ideally, any initial preparation should be done in early autumn, then the wind, rain and frost can work on the soil over winter. Ground so treated is much easier to work afterwards and even heavy soil will begin to take on a more manageable structure better suited to the cultivation of plants. In reality, it is not always possible to do the right thing at the right time, so you have to pick the most opportune moment. Gardening is always a balance between ideal theory and practical compromise.
Bearing these remarks in mind, the next stage is to turn over the soil roughly. Unless you have the type and size of plot which is most easily dealt with by tractor and plough, there are two courses open to you: hand digging and mechanical cultivation.
Hand digging is done using a spade, or, in the case of very heavy or compacted soil, a flat-tined spading or potato fork. The perfectionist will recommend some very laborious methods of digging which are guaranteed to put off a new or even a moderately enthusiastic gardener for life, especially if there is a large area involved. For most purposes single or double digging will be quite adequate. The former consists of inserting the spade as nearly vertically as possible to its full depth into the ground, bringing up a spadeful of earth, and then turning the spade over so the spadeful falls back into the hole upside down. This method has two functions — to introduce air into the top spit of soil, and to bury 9—12 in. (225—300 mm) deep any weeds on the surface. At this depth the majority will die and rot down.