-Use Speedy G
-Use cover/dark areas to ambush players
-Wait until they are in a gunfight and can't react to you
I found stealth killing idol carriers in Plunder and Team Objective to give consistent medals.
Play the block mesh maps. I always find it pretty easy to get stealth kills there.
----Greetings from Sony Censortainment Network Europe----
------------------Join my GTA V crew "ND forums"!-------------------
Play Syria if you could. Its darkness makes getting assassins pretty easy. I would say do this in Plunder and stealth kill idol carriers/guards. Its fastest. But if your not willing to do that, play TDM and just flank like crazy. I've gotten 3 assassins in 1 game of TDM, so its possible. Much more frusutrating as you'll have a limit on the amount of kills you could get before the match ends, but it is shorter.
-flank enemies, people who camp, particularly snipers are the easiest bait.
-personally I would soften them up with gunfire a bit, because of how buggy it is to register as a stealth kill, if i bring them down to half health with my gun from behind and then punch them it will kill them no matter what and still give you an oh snap. Nothing worse than smacking the back of a guys head and then getting killed.
-speedy G is great for catching up to people in the middle of a map and people in gunfights. If they are preoccupied with something else, then this is your time to get behind them and stealth kill.
-use the map to your advantage, if someone notices you and comes to kill you, then use this oppurtunity. Think of where they last saw you and expect for them to go to that spot, use the map to your advantage, climb out the window as they run up the stairs to look for you and then loop around behind them to kill them.
-all you have to be is behind them and off their camera, it may be a bit hard, but you can stealth kill people who know that you are there. rolling behind them and meleeing them in close quarters may get you an unexpected stealth kill.
Also, Syria is one of, If not the best, maps for upgrading cloaked, so vote for it if it shows up. Dark and small maps are always preferred.
Go for the idol carrier in Plunder as often as you can, as well as people in the middle of gunfights. Just go up from behind, wait for the blue icon and snap their back.
2. Use Speedy G with Bargain so you can run after an unexpected opponent & get a stealth kill
3. Stay hidden as much as possible and if you see an enemy, wait for them to run by, then jump out of cover and attack!
4. If a big battle is going on, stay in cover and stealth the remaining survivor(s) if there are any
This is what I do so I dont know if its the best strategy but it works for me