1) remove the number 1 spark plug
2) remove valve cover for drivers side
3) rotate engine over and watch the valves for number 1
4) when intake valve closes align the timing marks at 0 degrees
5) note position of number 1 plug wire on distributor cap
6) insert distributor so the rotor is pointing to the number 1 wire position(it will rotate as it drops in)
Make sure that when everything is set at 0 degrees you have equal movement (rotation) of the distributor in both directions, this will allow adjustment for timing. You can reset it 1 tooth at at a time to fine tune where the distributor is set. You may have to roll the engine over a little to align the distributor and oil pump drive shaft, this will make the distributor drop in the last 1/4".
Forgot to mention the reason for removing the number 1 spark plug is to check that the number 1 piston is at top dead center once the timing marks are lined up at zero degrees. Just use a pencil and insert the eraser end into the spark plug hole to touch the top of the piston to verify top dead center. the intake valve will be open while the piston goes down, it will shut and then the piston will rise for the compression stroke. When the piston is at the top of the compression stroke the spark plug will fire that is why you want it in this position at 0 degrees on the timing marks and drop the distributor in for the rotor button pointing at the number 1 spark plug wire.
The 4 strokes of a 4 stroke engine are: