More tips: Set Vehicle access to Everyone. Use cars that have max vehicle performance upgrades or the highest available (Armor, Engine, Transmission, Turbo, and a non-stock Spoiler). Stay together during the driving segment or go separately but CMC is a team effort.
Kurumas are NOT bullet proof. The side windows are vulnerable so keep the front or back pointed towards hostiles.
For specific missions:
Fleeca Job
Scope Out: Straight forward
Kuruma: Straight forward
Finale: Straight forward
Prison Break
Plane: Blow up the gas tanks ahead of time and clear the runway before taking off in the velum.
Bus: Destroy the police chopper before approaching the bus.
Station: Dial 911 for a police car to reduce unwanted aggression. The parachute method is fast but inconsistent in safety (pull the parachute too late, crash into the containers, etc). Just fight through and utilize the heavy armor to its full potential.
Wet Work: Alert Popov and kill him as he tries to run. Use the Karuma to finish the cops before picking up the deposition.
Finale: The Karuma can go inside the prison and make the shootout much easier. Here's a video on how it's done: https://www.youtube.com/watch?v=qybCcJS7EN4
Humane Raid
Key Codes: The garage is a good place to hide during the shootout. Don't run at it too quickly or the door will reset and will have to go through the entire animation again. Everyone can use the "Request Personal Vehicle" option in the interaction menu to have their car spawn nearby to use after picking up the briefcase. The vehicles CANNOT be used during the shootout because they spawn outside of the small mission zone.
Insurgents: Straight forward
EMP: The enemy jets target the Hydra PILOT so everyone can take off on the Lazers first. The Hydra Pilot can hop inside to spawn the enemy fighters, then eject and go below deck to stay safe as everyone else takes out the now harmless enemy fighters. The fighters will fly towards the carrier in a straight line and shoot towards the pilot (who should be safely below deck).
Valkyrie: Destroy the first chopper that spawns with a Homing Launcher and destroy the new enemy choppers as they spawn.
Deliver EMP: Stealth mission
Finale: The pilot and gunner can ignore the enemy ground units and focus on the choppers that spawn. There will be a total of 6 that spawn in waves initially, and then 4(?) that spawn after picking up the ground crew.
Series A
Coke: Do what works, there are many approaches to this mission including but not limited to: sniping from the pier, landing the chopper on the roof of the boat, escaping into the tunnels, escaping on the chopper, etc. Shoguns are recommended on the boat due to the blind corners and narrow hallways.
Trash Truck: The difficulty comes mainly from the time limit and how squishy everyone can be without heist gear. Top off health and armor between trash pickups. Work quickly but safely and efficiently. My teams have done it by having 3 provide cover and 1 grab the trash bags. Once all the bags are collected, the Collector joins the other 3 to finish off the remaining Ballas before moving to the next pickup.
Bikers: First part is stealth, the getaway has some RNG elements.
Weed: ignore the checkpoints and go straight for the target. Clear most of the Ballas but know that a small number do respawn. The escape also has some RNG elements.
Steal Meth: Clear the area of O'Neils before taking the tanker. The tanker has very little HP so fail the mission and restart if it's health is too low. Trevor mentions that some trucks are faster than others. The difference is tiny but the MTL Packer has a higher top speed than the Jobuilt Phantom but a slower acceleration.
Finale: During the escape, don't ram the Lost bikes. They have a tendency to explode and kill whoever drove over them.
Pacific Standard
Vans: Only the navigators have to do anything. The drivers can lounge around. Do not kill the van driver or the shooter will get unwanted stars. Stop the van by parking in front and jack the van.
Signal: Drive to the second set of Sea Sharks and leave a minimum of two Karumas at the beach. After collecting Avi, take the Karuma straight to the checkpoint, avoiding police along the way. A faster car can be used but that is a risk from getting shot by police.
Hack: Decoys drive to the site and kill the rival crew. Transporter goes the white van. During the escape, person in rear shoots back and the two in front shoots forward.
Convoy: Prioritize the enemy choppers. 3 in the Insurgent Pickup and 1 in the Barracks. DO NOT follow in a Kuruma as it is vulnerable to the choppers and increases the risks.
Bikes: There's a lot of RNG in this mission from the way the Lost NPCs spawn and from player variation. Stick together so in case someone falls off his bike, the other 3 can provide fire support. It's very easy to die even when wearing the Heist Gear.
Finale: All 4 exit the bank guns blazing. Don't worry about getting hit and losing money; there's a larger award in the end. Use the Kuruma trick to escape. Go straight for the Dinghy or follow the checkpoints. Both have their own pros and cons that is discussed elsewhere.
Source: GTA Wikia, Completed CMS 3x with different team members. 2 were perfect runs that we finished without failing once.