Check you're getting a spark. If not, check the ignition system methodically. Common points (sorry - that wasn't intentional...) of failure are the coil, HT lead from coil to distributor, distributor cap, rotor arm and plug leads (HT from distributor cap to plug).
However, getting a spark is only half the story. The spark has to happen at the right time. Distributor firmly clamped? Timing set up correctly?