Wheelbuilding setup

How do you know what is the 'right' spoke tension? This is my main problem when I've ever had to rebuild/true wheels. In the past I've put on too much tension and spokes *have *snapped...

What broken said, tensiometer is useful if you build lots of wheels, having said that its £70. Just use feel. I compare tension on another wheel which I know is OK.

Seem to be a lot of people only building front wheels on here.

Assumption based on what evidence?