a no spark issue can be caused by many things. the first and easiest thing to try is to install a new spark plug. if that does not help, the next easiest thing is to check the tail and brake light bulbs. if they are good, test the spark plug boot for continuity. then check the spark plug wire, points, condensor, and the charging coils. most often dirty or misadjusted points are your problem. on a point type system it is usually a good idea to take everything apart and clean it up. a small amount of rust on the stator plate or charging coils can cause a lot of trouble.
cdi type ignitions either work, or they dont. so if a new plug and good brake/tail lights are not the cure, then chances are the cdi is bad.
with both types of ignition systems, you still need to make sure that all wires are in good shape, connections are clean and tight, and all grounds are hooked up, clean, and tight.