Are you saying it cranks good, but won't start? Or it won't even crank? If it won't even crank, make sure the battery has a full charge and all connections, to and from the battery are clean and tight.
If it cranks good but won't start, do some of the basic tests. Have a helper crank it while you visually check for spark at the plugs. If spark everywhere, use a gage and check fuel pressure.