Find TDC of cylinder #1 by looking at the the valves and the timing mark on your pulley.

With the dizzy out of the car put the dizzy cap on (with the rotor in there a well) and mark on the outside body of the dizzy (with a marker or something) the centre of the number 1 contact (where you're going to put the number 1 high tension lead.)

Take off the dizzy cap and turn the rotor so it's pointing at the mark before sliding the dizzy back into the engine block. When you get toward the bottom the rotor is going to want to slide anti-clock wise (in the direction of the firing order) so you want to turn the rotor clock wise about 20 degrees or so. So when the dizzy is fully installed it is as close as possible to the mark you made before.

Put in the adjusting screw but leave it a little loose to fine tune the timing later. Install your spark plugs high tension lead and everything else you've disconnected.

Start the car and set your timing. I use roughly 10 degrees base timing at about 800rpm. Then set your dwell after that.