There is only one way to do this properly, and that is to use a strobe. If you haven't got one, borrow one from a friend but make sure that it is a xenon type which are much brighter (and more expensive) than their neon cousins. Timing goes hand in hand with the points gap so make sure you've set the points correctly first. Setting the ignition timing is actually quite easy once you've done it a few times.
First you need to find the timing marks which are on the crank case pulley. They are easy to miss, so I suggest you get your head under the car and have a good look. Rotate the engine with a spanner on the pulley nut until the marks are visible. You may need to clean them up a bit first. The type of marks varies from car to car, and there are diagrams in the Haynes manual. Generally, each mark represents 2 degrees before top dead centre (BTDC). Find out the timing specification of your car (it is different on 1.6 and 2.0 Capris). On my 2000cc Weber carburettor Capri, it is 8 degrees BTDC, and on the 1600cc VV carburettor Capris it is 12 degrees BTDC. Make sure you read Chapter 13 supplement of the Haynes manual which gives the updated settings! I suggest that you very carefully paint the relevant mark with a dab of correction fluid to make life easy for you (this will last the life of the engine). Now locate the timing pointer, which is a sharp piece of metal located on the top of the pulley. Place a dab of correction fluid on the pointer as well.
You are all set to check the timing. Attach the leads of the strobe to the battery terminals and the impulse lead to no. 1 spark plug which is at the front of the engine (re-fit the HT lead as well). Make sure all leads are well away from belts and fans and start your engine. The car should be up to temperature before you do this test. With the engine running, the strobe should be flashing brightly. Move over to the distributor and pull of the vacuum advance tubing which attaches to a pan-shaped advance / retard mechanism on the side of the distributor case. Point the strobe at the markers you painted. They will appear 'frozen' by the strobe and of course should line up. If they do not then you will need to adjust the timing:
Locate a bolt and clamp plate under the distributor. It is hard to find at first but is at the very base of the distributor enters the engine. Loosen off this bolt (about two turns) and with one hand holding the strobe slowly turn the distributor with the other hand (very small movements only!). You will see that the marks move, and the pitch of the engine will change. Align up the marks and re-tighten the distributor retaining bolt. The timing is now set. While you have the equipment available, re-attach the vacuum hose to the distributor and get someone to rev up the car. Watch what happens to the timing marks !
A few pointers here: if you find that your car is pinking a lot under acceleration then try reducing the timing by 2 degrees (e.g. from 8 to 6). If your Capri engine is retarded too much she will feel very unresponsive and the accelerator will feel strangely hard to push. Unfortunately, there is so little lead in 4-star petrol these days that pinking can still be a problem even with the timing set correctly.
With everything set OK, you will probably find that the engine tick-over needs adjusting. Find the knurled nut at the back of the carburettor and turn to change the tick-over speed. Set it to 800-900 rpm on the tachometer.