Signalling for Newbies

Is there a good straightforward reference on signalling for newbies?
My (LNER) layout is nearing competion of the track laying, the points
will be electrically operated, and I'd quite like to have at least
some signals!
I need to know things like how you'd decide how far from a point a
signal should be, and what the rules would be for deciding how long a
section of road should be. I am a regular train passenger, but never
saw how it was in the old days.
And yes, I know it's arse about face. As previously stated, with two
small boys (and one big one) in the house, playing trains is the main
focus :-)
Guy