1. Please leave people some time between missions in case they need to change loadout. A lot of hosts hop from mission to mission non-stop, which leads to some players sometimes using loadouts that are ill-suited to the upcoming mission.
2. Read the mission description and check the mission settings. If you are playing the campaign, read the mission description, it can save you a lot of hassle by telling you vital information such as where to search for certain things and what to bring.
3. If you are playing a mission at night, bring NVG and IR lasers for your guns. You can toggle the lasers on your guns with the B button and the NVG with N button. These two items will save you a lot of grief at night.
4. Use the UAV to recon the enemy locations. You can use Z to mark out enemy positions and then call them out over mic to your friends. While you unfortunately don't get any xp for the tagged kills, tagging out enemies can really help under default settings. Forewarned is forearmed. Also, if you die, be on the UAV watching over your surviving companions.
5. Use Ctrl to shout to enemies to surrender. While I am uncertain what determines how likely they will actually surrender, having them surrender can save you some ammo since you only have to restrain them afterwards instead of killing them. Plus, you get more XP per arrest as opposed to killing them.
6. Shoot out the lights at night (preferably with your pistol) as taking them out will make it harder for enemies to spot you and hit you, while you can see them perfectly fine with your NVG if you followed my rule of bringing NVGs to night missions.
7. You don't have to run everywhere. Sometimes, slowing down, scout ahead with the UAV then proceed might be better than just running blindly into enemy positions trying to gun everyone down. Also, sprinting drains your stamina and it will be harder for you to aim with your gun.

1. Most of the missions encourage using stealth so bring your silencers. Unless it has an integrated silencer barrel, you can always just remove the silencer should you don't feel like it.
2. You will go down quickly in a firefight even if you are wearing heavy plates and heavy helmets. This is (un)fortunately not one of those gun-ho games where you mow down rows and rows of enemies like Rambo movies. Always go look for cover should a firefight break out.
3. Unless you are wielding a submachine gun, you can hit enemies behind wooden cover/doors. If you come across a small room and you hear footsteps/enemy chatter inside, feel free to spray the suspected area with bullets. Better yet, if you/your teammate have the optical fiber camera, you can see where they are first and kill them with accurate bursts.
4. Using common weapons can be more advantageous compared to using more exotic weapons in the sense that it might be easier to find ammunition for them. For example, AKM and AKS ammo will be much easier to find in the field compared to AS-VAL ammo.
5. Having a good balance between protection and weight is important. While you want to go for stealth, sometimes things don't work out and you have to prepare for a prolonged firefight. On the other hand, carrying a heavy load will make it harder for you to aim and shoot after sprinting from cover to cover, thus effectively reducing your efficiency and costing you more ammo.