Well I am not a pilot and have actually never been anywhere near a Cessna. Most of the engine starting procedure is a mix of stuff from flightgear (free simulator), other simulator videos and stuff I read or watched online.
Perhaps the checklist is different for starting a c150 ? I can't imagine that it is too much different. All planes start with the battery doing a primer stroke and setting the magnetros + ignition, adjusting mixture and throttle release the brake and you are already flying. I have a more detailed description in the game comments down below, I would love your expertise on the accuracy.