Can I install a security system myself?
This is actually relatively easy - many hobby shops (eg Maplin in the UK) have kits which require very little technical know-how.

I guess the pre-requisites are:

Understanding your perimeter - 


use break sensors on the highest risk areas (doors and easily accessible windows)
use motion sensors in key hallways
do you include your garage
do you include external sensors
do you want to trigger a camera or similar


Control requirements - 


where will your control panel need to be?
should it have a panic alarm


Compatibility requirements - 


break sensors may be passive, or may be powered. If powered, what voltage is required
usually easiest to go with one brand throughout