I must be getting soft, so many USMC jokes ran through my mind...but being Sunday morning I decided to be nice
Seriously, nothing but respect for my Marine Corps brothers, some of my best friends are Marines,
With respect to going USMC from the Academy. This was an open ended question, so difficult to answer with any specificity, but a couple thoughts:
1) While at USNA , take advantage of the opportunity to talk with the Marines stationed at the Academy, both the Officers and Senior enlisted. Learn about their MOS, their experiences, etc. This gives you better insight into life in the Marine Corps than any recruiting video. Also, you need their vote of approval to be assigned to USMC from USNA. Finally, USMC is a pretty small community, so you may run across them when you in the fleet, and that past connection may prove helpful when you need something.
2) Keep an open mind. There are many who show up at USNA hell bent on becoming a Marine,,,,many do, and many don't. USNA provides a lot of different Service Selection opportunities, and you don't always get your first choice (although we try). Take your Navy professional knowledge seriously, it keeps the upper class off your back and who knows, knowing what weapons systems are on a LCS may prove useful someday. Even the principles of Nav class will be helpful when you do Land Nav at Quantico.
Good Luck....and remember that crayons have no nutritional value. (Sorry, I was trying so hard to stay away from USMC cracks).