First things first:
1. Check the fuel to make sure it does not have water in it!!
2. Check to see if you have a spark at each spark plug. Should bridge a gap of about 1/4" if good.
3. Plugged fuel filter??
4. Carburetor dirty and plugged? Kits available all over.

Electronic checks depending on motor at this web site:
outboard stators, ignitions, power packs, modules by CDI
Bill