You are already ahead of most people by asking the question before you go in, rather than after. That instinct will serve you well.
The first thing to find is a routine. However long your sentence is, boredom is going to be one of your biggest enemies. Reading was what saved my sanity, and it is partly why InmateAid exists today. Find whatever that thing is for you, whether it is reading, writing, working out, taking education courses, or learning a trade through prison programming. Structure your days around it. Inmates who drift through their time with no purpose do harder time and make worse decisions.
Stay out of inmate nonsense. This cannot be overstated. Whatever drama, conflict, or scheme is circulating in the unit, it is not yours. Keep your head down, do your own time, and let other people's problems stay their problems.
You will make friends, and that camaraderie genuinely helps. But be very careful about what you share. Never discuss your crime, your sentence length, your co-defendants, or anything about your life on the outside with other inmates. Ever. The saying that anything you say can and will be used against you applies inside just as much as it did in the courtroom. Inmates talk, and information about your associates or your finances can create problems for people you care about on the outside.
Learn the unwritten rules fast. Cutting in line, reaching over someone in the chow hall, sitting on another inmate's bunk, listening in on conversations that are not yours, these are all serious disrespects in prison culture and they cause immediate problems. None of it will seem logical coming from the outside world, but inside those walls it is the social code and violating it has consequences.
You are going to get through this. Go in with your eyes open, stay quiet, stay busy, and protect your release date like it is the only thing that matters. Because it is.