While setting up a digital piano in your home is a very straight forward task there are a few things to consider.
Putting it together
If you purchase a piano from a local dealer, they will invariably deliver it for you already assembled - that's part of the service. If you buy it online from a non-local dealer, it will arrive in a box and you will have to put it together. This is a straightforward task and assembly is not that difficult, but it is a two man job, especially when lifting the top of the piano onto the base.
Unlike acoustic pianos, digital pianos are pretty hardy and do not suffer from changes in temperature or humidity. They can therefore be positioned pretty much anywhere, even under a window or against a radiator. However, you should avoid direct sunlight as this will fade the cabinet, and avoid a location that means sharing a socket with another electrical appliance as this may cause interference. Of course, you also want your keyboard in a spot that encourages you to play. Try to find a place that is easy to get to, that allows plenty of elbow room and has good lighting.
A room and its furnishings will contribute to the sound of a piano, for example a wooden floor will make the sound more reverberant or lively whereas a thick carpet will deaden the sound. Many digital pianos enable you to overcome this by adding reverb or brilliance to the sound to suit your taste. Some even allow you to make changes to the sound on a note-by-note basis - ideal if you have a room or furnishings that allow certain frequencies to dominate.
When it comes to sitting at the piano, there are two things to consider; how far you sit from the piano and the height of the stool.
Sit on the front edge of the stool with both feet firmly on the floor. If you can comfortably touch both ends of the keyboard with only a slight feeling of stretch in the chest then you are sitting at the right distance. In terms of height, an adjustable stool is best, but if not a cushion is fine - make sure that your forearm and wrist make a straight line.
Finally, don't leave your digital piano turned on when you are not using it - not because of any risk of long term damage but because of the waste of electricity. Some digital pianos have an auto off feature that switches the piano off after a period of inactivity. This is great if you have kids that play as they are the ones that invariably tend to leave the piano on after use.