This is for a non boosting method.
Obviously, you should put Pulse Grenades in your loadouts and equip the Explosives support upgrade. This will increase the radius and damage the grenade does, making it hopefully easier to get kills.
You only get 1, so if you're going for this don't be afraid to choose them if you get them in ordinance drops.
Now, you're best bet is if you see a one vs one battle happening. Which is better in the FFA playlists. Try and throw your grenade right between them as they close distance when they both have damage. Try to only throw your grenades at 2 enemies. If you're in team slayer try to go for the initial rush to power weapons, like the rocket launcher or sticky detonator. Objective gametypes will also likely make a team group together.
Keep at it. This will happen more by luck than skill. And if you're unsure, most of the damage of a pulse grenade come from the pulse at the very beginning and end of it's life.
EDIT: credit to Lazyslothboy001 I completely forgot about the grenadier mod that allows you to carry an extra grenade, which would start you with 2 pulse grenades.
Edit2: You can get this with two thrown pulse grenades, you just need to get the kills with the pulse grenades.