Expert Ninja Trophy in Uncharted 3: Drake's Deception

Stealth Kills are taught during Chapter 5 and are basically a melee attack whilst remaining undetected which results in an instant kill. The tutorial itself will not only show you the different ways you can attain a stealth kill but also credit you with 4 of the number required, after the final kill of this sequence which is the guy you drag over the table backwards (kill number 4) then restart the checkpoint to begin again. This is a safe and steady method to get 5 kills in a row but there's a slightly better and faster way to do this in Chapter 8 - Citadel.

The Citadel method begins when you reunite with Cutter and Chloe, after a brief cutscene you will regain control and you are able to jump down by pressing to stealth kill the first guy. You'll see the next one leaning back against a rock, crouch behind it and hit again for kill number 2. Stay where you are and a guard will come by and patrol before turning his back to walk away again. Hop out of cover and chase him down and again melee him to break his neck, and run around the corner to the left to jump another guy for kill number 4. By now the other guys in the area may well have taken notice, though it's possible to get one more on the guy up the small flight of stairs but he is hit and miss. These kills are all in very quick succession and the restart checkpoint places you back to the beginning just before you jumped down on the first dude. This is a perfect farming area for stealth kills should you need them for Master Ninja due to the quick turnover of kills.

Here's a video of this method courtesy of PowerPyx: