If you had a chance to speak with cadets and/or midshipmen before they commissioned, what wisdom, advice, and lessons would you offer them?

The title says it all: https://blog.usni.org/posts/2017/08/10/leadership-means-listening

Earn it everyday! Remember it is service no matter how senior you get. Start and finish each day with gratitude and never forget where you came from. Lead by example always in all things.

Get qualified, be a productive member of the team. This has a lot of layers to it and its more than just getting qualified, its: learning the ship, learning the mission, learning the people, learning the Chain of Command, learning the TTPs, and integrating with the crew. They are your family. They are your support network. Learn from everyone. There are lessons to be learned everywhere, you learn from both good and bad leaders.

Your Chiefs' have technical knowledge and experience you don't, integrate them into your routine, but remember they are part of the decision and not the decision maker. They aren't infallible and sometimes their goals don't align with yours. That's OK. Your job is to leverage their experience to help inform decisions.

Always remember "show me the reference" - this isn't because you are micromanaging. It's so you learn where to look and so you can provide backup to your sailors. When in doubt the pub has an answer from where you can start.

Remain humble.
Keep your paperwork squared away.
Lead by example, maintain your professional integrity.
Remember that people are watching you even when you're off the clock and therefore you may hold yourself to a standard higher than you were when you were an enlisted individual.
Read and study. Find those courses that provide you with leadership guidance and take them all, just not at the same time.
There's no gold stars for flaunting your intelligence, listen first to the question in its entirety before responding.
Try not to engage in a war of opinions. Stay objective and only deal with evidence-based data.
Don't be afraid to say I'll get back to you with an answer.
Treat your colleagues with respect and you're enlisted with more, for they are the shoulders you stand upon and one kind word goes a long way.

Start developing your leadership philosophy now - if you don't, one will be given to you. I was a CPO prior to commissioning, but I was still an Ensign after I commissioned. Don't go in making changes, let dust settle, learn & evaluate, work with your enlisted leadership team and make the place better.

Listen to learn vice respond. This allows you to earn trust, give respect to your people and show that you care.

Always remember to value your people. Always remember character; moral courage, honesty, humility and empathy.

I teach leadership via the RBLP certification program, look at it, there is a lot of good info in it and COOL pays for it.

You already know this, but listen to your chiefs and let them run shxt! Also, not all enlisted who get commissions make the transition. Of the few former chiefs who I've seen, they've done well, though. Always look out for your people and they'll look out for you.

I was fortunate to have several "mentors" who were senior to me in years, but not rank. My first Master Chief assigned to me was a fountain of wisdom, great teacher (after he realized I was serious) and the most adept scrounger of anything and everything we needed (this was Viet Nam).
Today's military is much more internally/externally political than before, and career ending (unless you like Iceland in the winter) so think before you speak. The seniors above you, know your history and it is your job to be an asset to the unit in your new position...time and experience and OBSERVATION of the unit's dynamics are your playbook.
You have to earn your position by being an asset and if a conflict arises, then be as diplomatic as possible about the potential conflicts on ALL aspects.
Good luck....many of my my senior enlisted and superior Officers are among my best friends.

Leadership is leadership, and as an officer you will instantly find yourself in that role. There are plenty of great books on the subject written by civilians, and spending the time to read some of the better ones and absorb that knowledge will provide you value regardless of which role or unit you are assigned. If you look at successful individuals in any organization you will typically find that they are well read.

Talk less, listen more. Accept criticism, but do not accept disrespect. Put your team first, yourself last. The only way to get better is to do, so accept tough tasks, try hard, ask for help, don't be afraid to fail. What your boss finds interesting, you should find fascinating. Contrary to what some NCOs have written on here, they do not know more than you do about everything, and they do not know everything. They're not all geniuses. There will be times when neither of you knows exactly what to do. Work together to figure it out. There are as many bad NCOs as bad officers. Be receptive to good advice regardless of where it comes from. When you make a decision, you have to both stick to it/enforce it, and be willing to change your mind. That's one aspect of the art of leadership.

Watch band of brothers.