Battery or Mag ignition?
1. Drain the oil and replace with new
2. remove the valve cover and make sure none of the valves are stuck.
3. remove the spark plugs (note the firing order) and squirt some oil into the cylinders and then turn the engine over with the hand crank (if available) to recoat the cylinders
4. Check your wiring (plug wires, others)
5. check under the distributor cap to make sure it is clean
6. drain any old fuel; put some new gas in and open the carb drain to see if you get a good steady stream (dripping is not enough) you may have to clean the fuel system, and the carb (if gas was sitting in the carb when it was last parked)
7. try pulling it around with the fuel off (prime the oil pump and get everything relubed
8. turn the fuel on and try pull starting it