I just finished one of the GTA Heist which is Prison Break with some of my pals and I thought I have a few tips for you guys that will make your life a little easier. If you like to figure things out on your own then you should stop reading now. Overally this heist is not hard as long as you communicate well with your teammates and coordinate your actions well. The tips I'm giving are to help you in case you're stuck on any of the setups or the finale and want some advice.
#1: In the setup mission where you have to steal a Velum, It is a lot easier if one of your teammates have the Armored Kuruma (unlocked after the first tutorial heist). All four of you just get into the Kuruma and shoot from inside. This way you reduce your chances of dying to the minimum as the Kuruma is really tough and will protect you and your teammates from the gunfire (There's a lot them).
#2: The setup mission where you have to steal the prison bus is pretty striaght forward: steal the bus and lose the cops. The only tips for this one is take out the excort helicopter as fast as you can with a homing launcher and go off-road once you are off the sight of the cops.
#3: In the setup mission where you have to steal the police cruiser while posing as cops, call the cops and steal their car is the easiest way. Only kill the cops whose car you're stealing because you don't want anymore than a three stars wanted level. (P/S: I did not do the other team's mission so I can't help you with that one. Figuring it out yourself is part of the fun too.)
#4: For the one mission where you have to take out the lawyers at the city hall, just follow the instructions and time your shot (coordination is crucial) and you'll be fine. An armored kuruma (if you have one) will help you a lot in getting out of there alive. As for the other team who has to take out the target at the mansion, snipe the two visible snipers and another visible guard first then one of you try to stealth infiltrate the mansion killing the guards and target (not that difficult to do alone, use silenced weapons) while the other stay near a vehicle in case the target is alerted and try to escape. Chase him down and kill him with any means necessary.
#5: Now for the finale. For the pilot, when you almost reach Sandy Shores airfield you'll get 5 stars wanted level and jets will come after you and you have to stay alive until the prison team is done. To avoid being shot at, smartly maneuver your plane to follow the jet at its tail and you won't get shot at, EVER.
#6: For demolition, after destroying the bus get to the buzzard. While they will tell you to help the pilot out in destroying the jets, you don't have to do that as long as the pilot follows the previous tip. So stay near the prison (not too close or you will fail) and prepare to help the prison team escape when they do.
#7: Prison guard and fake inmate, follow instructions. Eventually the shootout will start no matter how well you play your roles so be prepared. Prison guard should use the combat MG as I find it most useful (due to its longer range). Fake inmate should pick up any SMGs from the dead real prison guards and help killing the other guards. Use the covers often and don't run into the open. At one point you will see an armored police truck. Use it to escape the prison as it is bulletproof.
#8: Now you've successfully escaped the prison but you still have 5 stars. Demolition will have to help the prison team escape by blowing up cops pursuing the prison team. Pilot will lose the jet at this point and have to land at any airfield to pick up the prison team. Intuitively you'll know that Sandy Shores airfield is ideal as it is closest to the prison. Make sure you prepare the plane for take off (align the plane with the runway) before the prison team get on the plane. Fly off with the prison team to high altitude to shake the cops. Buzzard guy have to shake off the cops too. Then just follow the instructions and get your reward.