Cover the ways in, first
Before thinking about anything else, cover every route onto the property. The main entrance, any secondary gate or door, and any point along the boundary where access is easy.
If you only fit a few cameras, these are the ones.
One camera at face height
The most common failure is mounting everything high. High cameras give a good overview of what happened, but a poor view of who did it, because you see the tops of heads.
At least one camera near the main entrance should be at a height where it captures faces properly. Everything else can be higher.
Watch what is behind the camera's subject
A camera pointing towards a bright light source, a streetlight, a window or the low sun, will struggle. The subject becomes a silhouette. Look at what is behind the area you want to cover at different times of day.
This catches people out on west-facing positions in particular, which work fine until late afternoon.
Use corners
Mounting on a corner of the building lets one camera see along two elevations. On a villa this can halve the number of cameras needed for the same coverage. It is the single most useful placement principle for houses.
Cover the approach, not just the point
A camera trained tightly on a door records someone at the door. A camera covering the approach to the door records them arriving, which gives you far more, including direction of travel and often a vehicle.
Wide coverage of an approach path is usually more useful than a tight shot of a fixed point.
Do not neglect the back
Front doors get covered, back gardens and side returns often do not. Anyone who does not want to be seen will use the rear or the side. On most properties, rear coverage is more important than front.
Indoors
Cover the inside of entry doors, so anyone who has come in is recorded. Cover the route between floors if there is one. Cover the area where valuables are kept.
Avoid covering areas where privacy is expected, both at home and in a workplace.
For businesses
Cover the entrance, the point of sale or reception, the stock or storage area, and any rear or service door. In a warehouse, mount high for a wide floor view and cover the loading area and gate.
What a site check can confirm
Photos and plans can show a lot, but some properties still need a site check to confirm camera height, lighting, blind spots, cable routes and access. Where that is necessary, the final scope and price are confirmed before installation.