Like Old-Biscuit says, first rule of troubleshooting, ask yourself "what is not working" and work backwards from those items. The circuit breaker can be tripping from something as simple as a loose wire connection. I say simple but if fact these can very hard to find.
Most of your 120v is for outlets or heating elements. If your tripping a breaker at the gen-set you'll have a large search area. For a gen-set breaker try turning off all breakers in the panel. Gen-set should run fine. Then one by one turn on a breaker, start with the mains. When you trip the breaker you've found the circuit with the problem (not saying you can't have more than one). Now you have to check everything on that circuit. Don't forget to check the wiring connections on the back side of the breakers.
If it's a panel breaker this helps narrow down your search. A 50 amp system can just be one side which helps eliminate half of your system. Of course a system breaker like for a AC unit will require checking out that particular appliance.
For outlets, a quick visual look at each outlet for a scorched spot or maybe it will smell burnt. I have replaced several bad GFCI outlets. Check things systematically, start with the outlet farthest from the box and work back. With the breaker off (CHECK WITH A METER THAT NO POWER IS PRESENT) pull out the outlet and check for loose wires, scorched spot, melted plastic etc.
Average problems take more time to find than to fix. I hope this makes sense and is at least as clear as mud. Good luck and be safe.