CREDITS: Gtamen, Gtamen Discord community, Gtamen subscribers, KA_Wouter, CGH Channel, Zeeeeemo and many more.

General tips:

Armour and snacks. Always. Restock on them after every mission as they are extremely vital to your survival when doing Heists on Hard. All snacks cost only $1 in your Facility/CEO Office even though it says they're Free. (Pay attention to your money when purchasing them)

Teamwork and communication is essential. These new heists are much more difficult than the ones released in 2015 and hence you need to be on your toes, communicating with your team at all times in order to be successful. Use Teamspeak, Discord, or the ingame voice and text chat to always be ready for when the AI comes around the corner.

Purchase and use any of the Shielded Riot Helmets (not just Riot Helmets) in missions where you can wear Player Saved Outfits. They protect you from two fatal headshots, killing you with a third.

Use Tear Gas to block hallways and choke points where the AI can get you from two sides. Shoot them once and they'll fall to the ground, choke, and die. This will minimise the risk of your team getting flanked, especially useful in large open areas with minimal cover and infinite enemy spawns.

The Marksman Rifle Mk.II is the only sniper in the game that can utilise something that isn't a scope. This is especially useful for controller users as it can make auto-aim shots a one-hit kill. Also kinda OP in PVP modes.

Staying close to your team will regenerate their health if you're a CEO. Especially useful when you're bunched up together surrounded by lots of enemies.

The Weaponised Tampa can be used in every Heist mission where a personal vehicle is, so make good use of it to mow down large groups of enemies where needed. However, it's not completely bulletproof so you can get shot down and killed so keep an eye on your health and armour while using it.

The Heavy Revolver Mk.II with Incendiary rounds has a guaranteed chance of starting a fire. Use it to down enemies and let them burn to death.

Same case with the Marksman Rifle Mk.II, with Incendiary ammo may not kill enemies in one shot but it will down them and they will burn to death eventually.

Act I:

Prep: Ambulance

Call 911 on your phone and select the Paramedic option to have the paramedics show up to your location, then steal the Ambulance and deliver it to your Facility.

Lester has specialised dialogue for this.

Prep: Akula

Instead of following the checkpoint and going up the stairs, follow the corridor to the right where there's an elevator. It takes you up majority of the way and makes it much more time efficient. Oh, and you obviously use it to get down too.

Lester mocks you if you take the stairs and tells you that there's an elevator you can use.

To add to time efficiency, have one person go to Fort Zancudo and one person at LSIA. This ensures that the Akula won't spawn too far from both people, reducing the time taken to get to it. However, the spawn for the Akula is random.

Setup: Dead Courier

The team that collects the Savage attack helicopter, you don't need to do that part stealth. If you have a Kuruma or any armoured vehicle, stay inside it and kill all the enemies, then pick up the briefcase and make your way over to the Paramedic team.

Setup: Signal Intercepts

You don't have to use the Deluxos, you can use them to trigger a checkpoint, and perform the hacks in any vehicle after that. This can make it easier for if it's a team of 4. Two people can take two Armoured Kurumas to shoot down the AI in the back of each van, while performing the hack, and the Deluxo team can take out the vans pretty easy. (Keep in mind that the vans take a lot of sticky bombs or rockets to take down, but go down in one shot from a Deluxo missile) Know that for the offshore and air targets you will have to use the Deluxos, so plan it out before you do it.

When the targets are on land, either drive your Deluxo in front of the vans, or the passenger's side. This will make it impossible for the AI to shoot as they only have a cone radius towards the back of the van.

For when the targets are offshore, drive the Deluxo in reverse to hack the targets, it will make it nearly impossible for the AI to shoot you down and keeps you in close range with the boat as your speed is nearly same.

Or you can stay on the driver's side of the boats and the AI will have difficulty shooting you down most of the time.

Act II:

Setup: Avenger

Split into two teams. One team goes behind the orange tanker for cover, and the other goes behind the power box and crate close to the plane for more cover. Each team takes out the enemies on the opposite side of theirs, providing clearance to eachother and reducing risk of getting shot from weird angles.

Taking out the enemies on the level of the generators is easier if you're to the side and below them somewhat. Take cover behind the offices on either side and take out the opposite side of enemies first. Accessing the generators is possible from right by the offices so you don't have to worry about going all the way to the far end of the hangar. You will have to have one person go there to trigger the checkpoint though.

The thermal scope for the Heavy Sniper Mk.II will save your life. First do a quick scan in the minimum zoom setting to get an idea of where the AI is hiding. Then from good cover, take your shots one by one. Keep an eye up above as those enemies have lines of sight on nearly everything, but they're easy enough to shoot down.

Setup: Rescue ULP

Given that staying in the water tower is not mandatory, the lookout team can trigger the checkpoint then head to the hallway entering the Foundry and take cover behind a suitable wall. Enemies will always spawn outside and try to make their way inside, making it easy to blind fire them as they enter the building, all the while providing decent cover so your armour and snacks don't get depleted as quickly.

If you own the Barrage ATV or any personal weaponised vehicle that has manned guns/turrets, use it for this mission and make ULP take control of the turret. ULP is an AI hence AI's have aimbot and can make quick work of any enemy that gets near you.

Setup: Salvage Hard Drives

The RCV has mostly bulletproof windows except for some of the side ones. Use it as rolling cover while your team salvages hard drives to keep them from getting under fire by enemies.

The RCV is very bad at clearing a path, so try and drive around Nightsharks and most civilian vehicles. (Contrary to what the trailer showed)

Act III:

Setup: Rescue Agent 14

Juggernauts show up with the Thermal scope for the Heavy Sniper Mk.II. Be careful when shooting them down though.

You can mark Juggernauts with Incendiary ammunition. Useful if you don't want to use the horrible goggle vision that Lester gives you.

For the first 4 juggernauts that spawn after collecting Agent 14 on the North Entrance. Place down sticky bombs close/at their spawn point, and detonate them once they spawn. This should make it easier for them to go down and reduced risk of your entire team dying right off the bat.

Use the Kuruma in conjunction with before grabbing Agent 14 and when clearing a path for him, excluding Juggernauts. It is by far the most useful vehicle in the game for Heist missions and it can make the difference between you staying alive and dying last moment.

Setup: Khanjali

Get a tall vehicle and make your way to the wall closest (farthest south wall to the equipment) to where the Khanjali's parked. Take out the two enemies that are atop of the containers and vault over the wall to make your way to the tank. Have the rest of your team destroy the equipment then get in the tank, pick your team, and bring it home.

Finale:

For the hacking segment, the AI will target the hacker, but not shoot them until they are finished hacking. The rest of the team can hide in enemy spawn rooms or behind cover and wait for the hacker's signal to open fire on the AI. [Video pending]

To move between servers for hacking, use the upper levels of the control room, there are less enemies there unless you have to hack a server on that level, hence making it a quick way to move from server-to-server without getting under fire much from AI aimbot.