Assuming you have correctly set the points, proceed as follows:
1/ Take the plugs out first, which makes turning the engine over much easier. Now turn the engine, using either the fan belt or the starting handle until the marks indicated on the picture line up. Now the clever bit begins:
2/ You'll need a 5 watt bulb, as used for the tail light, and two wires, with crocodile clips on one end and the other end connected to each side of the bulb. A good way to do this is to have the bulb in a plastic holder, to which two wires can be attached.
3/ Attach one of the crocodile clips to the "C.B." connection on the coil. (If you're not sure which one this is, it's the wire that goes from the coil to the distributor) and connect the other crocodile clip to a good earth. [This is how the adjustment works: when the ignition is switched on the 12 volts run into the coil and out to the points, which, when closed, allows the 12 volts to run to earth. When the points open this route to earth is blocked, producing a huge voltage in the other winding in the coil, which passes to the sparking plug. We need to find at precisely when the points open, and the light bulb will lights this happens, as the 12 volts can't run through the points as they open, so runs through the bulb, lighting it].
4/ Loosen the bolt holding the distributor to the block, which will allow it to move. Switch on the ignition but don't start the engine. Using both hands g-e-n-t-l-y rotate the distributor one way and then the other, to establish the point at which the light bulb j-u-s-t begins to light. At this setting the points are j-u-s-t beginning to open. To confirm this is the right setting, remove the H.T. lead from the coil (to prevent the car inadvertently starting!) and rotate the engine through one complete turn. As the timing marks come together again confirm the light bulb ignites precisely at this point.
5/ Clamp the distributor bolt, replace the H.T. lead, and go for a drive!