If you smoke, it would be wise to quit; if you don't smoke, don't start. If you are overweight, lose weight. Prepare yourself so that you can get a good grade on the ASVAB. Talk to a Navy recruiter now if you can and ask for advice.
you will need to be in decent shape to pass boot camp. You will need to be able to run at a pace of a 6 minute mile for at least 1.5 miles. You will need to do at least 60 push-ups in a row, and 60 sit-ups in a row also.
Get to those points and you will be OK. Also learn the phonetic alphabet and the 11 General Orders of a Sentry you will need to have both memorized and if you do so ahead of time it will help you stand out from the other recruits. Are you in the Delayed Entry Program? If so, you should receive a study guide.