Just to add my personal touch to Lavindathar solution :
It is a subtile mix of "taking you're time for headshots and rushing at the same time". Because even if you don't use ENGAGE feature, your squad still rack some kills, not as fast, but they will. So you need to be fast and precise : headshot while rushing.
I used M39 EMR / FAMAS combo. When armed with FAMAS, still focus on headshot. Worst case, burst fire above the enemy head and aim down if you miss at first. This will prevent you to make a body kill by mistake.
I finished my run with 20,800 points. Here is the score breakdown to give a idea of that you are aiming for:
* 118 kills
* 1 Melee
* 73 Headshots = 61% of my kills
* 11 Multi kills
* 7 Adrenaline kills
* 19 Streaks kills
* 47 Squad kills = 28% of total kills ---> 47/(118+47)
To save time, evaluate if you need to restart the mission or checkpoint by keeping track of your score breakdown :
* You should keep your kills vs squad kills to a 4:1 ratio...if at some point you are at a 2:1 ratio...it is not going well. You need to push a bit more...get kills before your squad.
* Before the tank portion of the mission you should be around 80% head shots kills. The ratio will drop later because you will get around 20 kills using the tank. Keep it above 60% after the tank portion of the mission.
Personal tips:
* The tank portion of the mission was completed using the tank...not on foot...so it is feasible to achieve 20,000 points using the tank. I know some people suggest to use the RPG. I did try this method, the tank portion take you way more time to complete.
* When you are about to get a headshot and there is only one enemy is sight, try to reposition yourself in a way you can see and kill two enemy...racking a couple of streak kills.
* When you reach the hangar at the end, don't camp at the top trying to get headshots...the suppressing fire of the enemy will constantly throw your aim off. You will loose precious time and your squad will kill the enemy. Get on the main floor, rush and headshot as fast as you can.
Conclusion:
I know that some gamer reached more than 24,000 points optimizing the run. 20,800 is not a world record...but I did it pretty effortless using this method.