Prior service to ROTC (and its subsequent commission). Any tips?

ROTC uses the Ranger Handbook as it’s “training Bible”. Being a former infantryman you have a leg up in that regard. I don’t suspect the coursework will be an issue for you.
I was enlisted for a little over 8 years before I commissioned via ROTC. The thing I’ve see trip up prior enlisted cadets are the inability to get out of their enlisted mindset/checking their ego at the door.

Remember that the moment you become a Cadet you are just that.....a Cadet. You are no better or worse than the other Cadets. All cadets, whether prior service or not, are not your subordinates. They are you peers. They will look to you for guidance as a prior service soldier unless you give them a reason not to.

I hope you pursue and successfully complete ROTC. I look forward to welcoming you to the Officer Corps.

I did not commission that way, but I know most of the rules. First, as prior service with an MOS, you are exempt from the first two years of ROTC. That means you can join in your Junior year, attend Advance Camp, and commission at the end of your Senior year. I've had senior ROTC people tell me that you should do all four years since the cadre will get to know you better, but all the prior service guys that
I know that joined in for their Junior year all finished at the top of their classes and got their Active Duty assignments. I'll let you be the judge on which you think is best.

BTW, if you didn't know this already, Active Duty slots are competitive and how many they have for each class is Needs of the Army. If you plan on going Active, you will need to bust some butt and finish with a high class ranking.

One other thing to think about is the Simultaneous Membership Program. You can re-enlist in the Guard or Reserve, apply of ROTC and join as an SMP. You get the experience since they should be letting you shadow or function as an officer, you get paid as an E-5 to drill, and the time counts toward TIS and to a degree, Retirement. I personally recommend the Guard, since most states have tuition assistance or some extra educational benefits. Your membership does not effect your ability to go active as long as you don't take a GRFD scholarship.

I already had a 4 year degree when I enlisted, so back then that limited my options. I can tell you that I would chose the ROTC route in your shoes, OCS is a royal pain in the ass and I disliked all my TAC's.

I am a prior service officer who commissioned from ROTC. As mentioned below, check with the desired college about ROTC availability and likelihood of admission. There are many former NCOs who become officers from ROTC, but there are requirements that need to be met (e.g. age, medical status, academics, PT testing, etc.)

https://www.goarmy.com/rotc.html