Today's wikiHow is useful for church secretaries...
even if it is called How to Survive in Federal Prison.
Really. I learned these same things during my tenure with the demented coworker from the hubs of hell. (she's long gone but I still suffer flashbacks...)

Bite your tongue.

Try to find out as much as possible about how the system works.
Ignorance of the rules is no defense. Information is power.
Do not be overly friendly with your cell mates coworkers but do ask some questions.

Don't tell people anything they don't need to know.
What starts out as a petty argument over a trivial issue can turn into someone bearing a strong personal grudge against you. Don't be paranoid. Just be aware that things may not be what they seem.

Always be polite and respectful to guards and other prison employees all co-workers, even if they are evil SOBs. That's because if you piss them off, they are holding all the cards and can make your life harder than it already is. So, don't give them a stick to beat you with.

Don't get a reputation as a "snitch".

Respect other people's personal space and NEVER allow others to invade your personal space. You will be tested and if you allow others to get too close to you for comfort, they will just get closer and closer until your subservience is obvious.

Above all, remember that the normal rules of the outside world simply don't apply any longer.