First, there are a lot of overbroad , generalizations about how a MOC makes his/her Nominations here... the truth is, there up to 535 different amswers on how to with their MOC. Some MOC don't have any involvement, some are very active, and I think I heard of at least one that didn't exercise their right to nominate because they were anti-military. That said, a couple thoughts:
You don't need to "cultivate" a relationship with the MOC -- in fact, trying could be counterproductive. The MOC isn't looking for a friend, they are looking for the best people that can represent their State at the Service Academy, and serve as Officers in the USNA. That said, it helps to "stand out from the crowd", especially in the more competitive states that may have hundreds competing for a slot.
How do you stand out ? First, show the initiative and reach out to the MOC office early --let them know that you are interested and working toward appointment to a Service Academy. Much of the advice about initial contact with you BGO applies , do you homework, ask intelligent question, etc.
Second, as CAPT MJ noted - participate in the MOC Academy day events --several of them are virtual now, and easy...but one of my Senators held a few around the State in the past, and I saw candidates go to multiple events. When attending, take the opportunity to meet the MOC (if available, my Senator was very engaging and took the opportunity to speak with each of the Candidates as well as the Service Academy reps. Finally, and most important -engage with the MOC Staff. There is no "just staff," even the receptionist in the MOC office. This is a good life lesson --you will quickly learn that treating the staff well goes a long way in getting influence with the boss, no matter the context.