What Advice Would You Give Someone Joining the Navy for the First Time?

My boyfriend (26) was accepted into the Navy today, and we're both excited for this next chapter.
For those who have served, what advice would you give someone before they ship out? What are some things you wish you had known beforehand? Any tips for boot camp, choosing a rate, military life, finances, deployments, or setting yourself up for success in the long run?

We're looking for honest advice, both the good and the challenging aspects of Navy life so he can go in with realistic expectations and make the most of the opportunity.
Thank you all for your service and any guidance you're willing to share.