I pre-wired my house for an alarm since the alarm got fitted at the very end. I figured it would reduce the work required for the final install. I installed wires for the motion sensors, reed switches for under-house access, the control panel and the siren. From memory, some units require 6-core (such as the control panel) and some 4-core so I think I just ran 6-core everywhere.
Since I knew the alarm I was going to install and knew where the sensors and control panels would be, I ran the cables to those locations and just left them there to be plastered over.
For the motion sensors, I had roof access so it was easy to poke a hole though the ceiling at install time.
For the panels, I positioned these near light switches. At install time, it was easy enough to locate the cables (near the power lines) and pull them though the hole in the wall used for the control panel.
The reed switches were under the house so also easy to wire up.
The alarm unit also required a phone line and power. Part of my plan was the location where the unit would live so I ensured the sparky wired phone and power to the appropriate location.
I had an alarm guy install the actual unit. Having the wires pre-laid reduced costs, though he added a screamer to the system.
I did not bother with window or door sensors since I have a lot of windows/doors and the motion sensors will trip once the guy enters the house anyway.
BTW: I put coloured PVC tape on the wires at 2~3 metre intervals to make it easy to identify what cables went where.
BTW2: I have a (renovated) 1920s house with sizable cornices. In one location, the plasterers incorporated the senor cable into the cornice, allowing the sensor to be attached to the wall rather than hanging from the ceiling. This looked a lot nicer, I wish I had done it everywhere.