Chris's Campaign Chapter 1-3 Rooftops.
What you'll need:
Flash Grenades,
Ammo in your MP-AF
Normal Difficulty
Start the chapter. Pop a shot in the first guys leg. He should run off to the side or down the stairs towards you. Throw a Flash behind him and have him stunned. (I aim for the steel beam in the middle, stuns both enemies.)
Run up to him and finish the job with a RT prompt. If the guy up top has ran down the stairs. Throw another Flash. Prompt then reload the checkpoint. Should take about 10 reloads to grab both achievements.
If it fails. You'll get a notch towards "Give A Little Push"
It's not perfect. Though you can knock both achievements out with this method.
Major thank you and credit to BLAZE VII for the 360 guide to this achievement and tips with Flash grenades and Normal Difficulty!
If you find a better spot to gather this achievement, let us know in the comments and I'll update and credit! Hope this helps!
EDIT: incorrect Chapter. Thank you Dragonborn Gear!