Here`s one of the best jail guides available: (it was written by Kumcho_Vulcho a while back)
Ranks: Bitch (0 earns) Schooled (70 earns) Mule (100 earns) Hardrock (110 earns) Lifer (150 earns)
Normal Earns: Laundry Work - Used from Bitch till 90% Schooled Kitchen Hand - Used from 90% Schooled to Lifer Workshops - Used at Lifer (gives good stat)
Special Earns: Make Shank - Used to whack (gotten after about 6 goes) Dig Tunnel - Gets you out after around 6 goes
Normal Earns: To reach Lifer you will need about 24 hours of jail time. To unlock Stuffing you will have to be at around 10% Bitch The fastest way to rank up is doing earns from Duties and Stuffing. The best duty for gaining rank is Kitchen hand, but Workshop gives you alot more cigs! Kitchen hand is unlocked around 90% schooled.
Special Earns: Make Shank will get you a shank after doing the earn about 6 times, 4mins per go. Dig a Tunnel will get you out after around 10 times, also on a 6 minute earn timer
"Aggravated Crimes": Stuffing and messaging will be performed via the agg timer taking 20 and 15 minutes. Pinching smokes, stealing contraband and walking the dogs takes 30mins.
Jail Time: This can be seen under the timers. It can be reduced by: Get blazed -heroin shot takes 20 minutes. However this is dangerous and should only be done in emergencies. Drink Booze - Drinking whiskey takes 4 minutes Smoke Cigarettes -no need to explain takes 3 minutes. Read Porn -no need to explain takes 4 minutes. Taking Contraband, gambling and trading Contraband is done via the case timer and can be performed every 3 minutes.
WARNING: Taking Heroin can resolve in an overdose and KILL YOU Rioting will get you killed by city leader for messing up PD
Gambling: This will be unlocked at 40% bitch. Buba will win more often then you however if you win you double your bet.
The Parole Board: Can't free you if someone tried to JB you and failed or you have been JBed and a cop returned you. Also if you got caught with contraband or whacking/GBHing another inmate. To get out, you must have actually served half your jail time, so it is not when your time until release says half, it is when you have acutually spent half your time in jail.
Conflict: From there you can steal cigarettes and Contraband and of course whacking. You will need a shank which can be made from Make shank earn or traded from other players. You can also Riot from there. You can also Walk the dogs this is Jail GBH which will be unlocked at 60% Mule
Jail Gym: The Jail Gym is a workout that gives some jail EXP. It is recommended you start doing this at about Schooled as you will often fail it until then. However it gives more jail XP than stuffing so if you don't need contraband use it after Schooled. It is on a ten minute timer.