What recommendations do you have for preparing an MS3 for ADV camp and MS4 year?

CPT (Join to see) learn land nav and troop leading procedures.

For ADV camp, have no distractions, personal, medical, mental, physical. Go in understanding the task is mission completion, much will go wrong along the way..deal with it and move on... You can not stop a squad cadet in your small group from getting lost on the patrol lane. You can be a good follower when not in charge, offer help if asked and be ready to take charge when the leadership changes at the end of the lane.

If you do not swim well, get in the pool NOW... CWST is not a mountain, but it is sometimes a sink hole..don't find out what its like the first time at camp. Dont be that cadet I have to drag off the pool bottom,,,,Im old,its get tiring for me as well to swim for two.

The APFT taken at the beginning should be the easiest morning of PT you do all year..if its not, work harder NOW.
You want an extended PT score, not just pass.

You will be told you can not be "forced" to due some of the physical tasks, thats true..its also a fast way to the bottom of the list come time for commission and branch selection.
Know the tasks to be completed before camp....if you have a fear of heights, water, being tired, long walks with light rucks, public speaking, land nav, understanding assuming a leadership position, basic patrol OPORD. Be as wiling to clean the toilet as you are to task others to do so.

Did I mention NO distractions... not from home, not at camp... You can get laid and drunk AFTER camp....let the boys and girls get caught up in that, hang with the leaders , men and women.

Get in good shape, master basic soldier skills, especially land nav and BRM, become proficient at TLPs, learn that being a good follower and supporter of the chain of command is just as important as being the guy in charge. TACs can see through bullshit, and know when someone is a spotlight ranger or a team player.