You will firstly need to beat the game and unlock:
-Taser
-Borescope
-Sensor Grenades
-Lockpick
-Flashbang

I got all A+ and so can you!

You should always have
-Taser
-Sensor Grenades
-Flashbang
-Breaching Kit (They are like flashbangs)

Your partner should have:
-Lockpick
-Flashbang
-Breaching Kit
-Sensor Grenades

-Tasers will one shot anyone.
-Sensor grenades will be needed to quickly assess multiple rooms.
-Flashbangs are needed so you can rush and melee people in rooms. Order your partner to flashbang a room by holding right clicking the door and releasing flashbang. They're very good at it.
-You can use your partner's sensor grenades if you're out. I enjoy throwing sensor grenades so that they're perpendicular to the hallway. This is so they only bounce in a small pre-determined zone.
-Breaching kits act as flashbangs, if you're out.
-Lockpicks are required to open doors without alerting enemies. Hitting the door will cause the enemy to be alert and they will shoot you faster.

About Bad Equipment
-You'll have 1 extra slot per person. You can choose what you need.
-Do not use the Heavy Armor or Shield. They will slow you down.
-Tear gas and smoke grenade are unnecessary and will slow you down.
-First aids are unnecessary because if you get shot, you will just restart immediately.
-Defibrillators are unnecessary since you will not be killing anyone.
-Pepper spray is not great. The range is pretty bad. You might as well just use melee.
-Gun accessories are unnecessary because you will not be using your gun.

To get A+, you'll need to RUSH with near-reckless abandon. Run whenever you can.

Melee
Melee is a hit or miss if you don't know exactly how to do it.
-Melee works better if you are running right and expect to melee something that is directly to the right. Do not try to melee in a direction that is not right.
-If enemies are stunned, you may want to stop running for a brief moment and then look at the suspect, and then melee once.

Be Mindful Of These
-Do not bother using your guns. No ally or enemy is allowed to die. Use the taser and taser-melee.
-If anyone gets killed, restart the mission.
-One melee will cause instant surrender.
-Always capture everyone alive.
-If you get wounded, restart the mission. You get point deductions for being wounded.
-I do not use the yell function to avoid alerting the enemy.
-Always get all the evidence and guns.
-You may have to restart the mission a few times to get the optimal randomness.
-Never melee the door unless there are zero armed enemies behind it. It will alert the enemy.
-You can melee non-civilians up to 2-4 times before they die. Great for interrogation. Civilians may take less hits.
-Watch those corners and behind the door!

Your buddy
Your buddy is terrible at combat. But they're very good at carrying extra equipment and throwing flashbangs. Keep him out of harm's way at all times.
-Use your buddy's door-camera to spot the enemies if it's a big room. Try to use this if the room is pretty large or if your buddy is idling.
-Use the motion sensor grenade to check multiple rooms quickly.
-Try to utilize both cops at 100%. They both must be doing something at all times. For example, I'll rush a room, melee a suspect, get the gun, and then order my buddy to arrest the person. While he is arresting the person, I will do something else. When he is done arresting, I order him to come back (with space) so that he doesn't have to travel so much.

Handling Civilians
-Watch out for dangerous civilians. Do not take your eyes off of them until they're arrested. The briefing will say if there are fake civilians.
-They may also drop a gun after they're arrested. Get it for more points.
-I normally melee them once so they surrender. You can also yell at them but I avoid yelling since it may alert the enemy.

Handling super soldiers
These enemies are super dangerous and their reaction time is insane. If they are unalert, you easily deal with them.

-If they don't spot you, you can walk up to them and then at the last second, rush and melee.
-If they're in a new room and they're close to the door, you can easily rush and melee.
-If they're in a new room and they're far from the door, use a flashbang and then rush and melee.
-If they do spot you, pull back. If they try to rush you, camp around the corner with the taser or melee. If they don't rush you, you'll have to use a flashbang on them.

-ALWAYS avoid alerting the enemy. Do not use gunfire and do not break down doors.
-ALWAYS use the lockpick. I normally get my buddy to use his.
-ALWAYS use a taser against these guys since a taser is one-shot, 100% accurate. Try not to immediately use tasers if you can just rush and melee since ammo is very limited.
-Guns are terrible against these enemies because 1 shot is generally not enough.

Handling regular enemies
Just like super soldiers except you can easily rush at them for a slightly longer time. If they're far away, use the taser or use the flashbang. Very easy to take care of.

Spotted? Use magnum bullets behind doors
Once the enemy spots you, they will trigger the "kill me" trigger. Go behind a wooden door and shoot through the door safely with your magnum bullets.

Stealth over everything.

Rush and wack to win!

Restart until you get a good RNG.

Here's a preview of me playing.

A better run of the last level: