What is the best advice you would give to an individual getting ready to be promoted to Sergeant?

First and foremost, your soldiers come first. Period.

Secondly....you're a Seargant not an E-5.

I would tell that Soldier to act like a SGT and not an E5.

As an NCO your prior peers are now you subordinates, act accordingly and realize they are no longer your friends, business is business. Be a leader and set a good example, know the standards and live by them. The Soldiers follow NCOs more if the NCOs do not mind getting a little dirty with their troops. Soldiers and mission is important, there will be times where you have to make tough decisions between mission and Soldiers. Be able to stand by your decisions and the consequences or rewards that come with them. There will be a lot of late nights you will have to work and weekends. Be tactically and technically knowledgeable and ensure you can train Soldiers. Good luck.

A couple things:
1. Be prepared for the dirty looks, etc from those who think they should have been promoted, not you.
2. Act like a SGT. That means adhering to regs etc BUT ALSO use common sense.

I've never heard of a promotion to "E5". This will be your first lesson, you are not earning a pay grade, you are earning a Rank in the US Army. The rank of Sergeant comes with many responsibilities, I could write a book on advice for you, rather someone has already done this.

1. Read the ADRPs (all of them)
2. Get familiar with AR 600-20
3. Ask those to your right, Staff Sergeants and Sergeants First Class, if you have doubts.
4. Never pass along information that you are not 100% is accurate. i.e. the crap you heard from someone. By now you should know how to research, so do it.
5. Always behave in a manner commensurate to your Rank. You represent every NCO that has came before you and those who will be following. Do not be responsible for giving the Corps of NonCommissioned Officers a black eye.
6. Always communicate with your Soldiers, your leaders book should have more information than the credit bureau.
7. Own up to your mistakes as you will make them, we all have.

Everyone makes mistakes, even sergeants. Learn from your mistakes, and do not make the same mistake twice.

Oh, and don't forget. If you need advice - there's LOADS of it right here!

If you know for a fact you're getting promoted, then first I wish you congratulations. Next, as has already been mentioned multiple times act, and be a Sergeant. To differ from everyone else's advice: remember that you are human, and that you will make mistakes. How you recover from those mistakes will say a lot about you as a leader to your peers, your junior soldiers, and the higher-ups.

Never abandon your principles, and never forget your roots. Remember, too, that you are no smarter than yesterday: keep learning through active listening, reading, and going to every school or seminar you can attend.

Expect the unexpected. Besides all the stuff you have in your FM and TM that may be asked know what is happening in the world just in case they ask you about world events or your opinion about it and what you would do if you deployed . The questions and topics of rally point on international attacks by ISIL, North Korea threatening the world with nuking the USA and that there are now Marines in Iraq is a good thing to know. Some may disagree but it will never hurt. You are MP (me too) so you should be proud. Who knows if they ask you about this high-speed female MP Sergeant that won the silver star by fighting insurgents in iraq and killing many by going into the trenches and throwing grenades when her convoy was ambushed by about a platoon size element of terrorists in Iraq? Be ready!
https://www.youtube.com/watch?v=2y5Ld_zx_zw