For starters, you will need to complete the Torvin quests that unlock the Wormrot Oils (for poison) and the Numenorean Fire (for fire). Once these have been unlocked, simply jump off of a raised area such as a tower, and then press A and push forward to glide. Outposts or the fortress at Shindram make for good locations as they are full of orcs, so you will have more targets.
Just to confirm, you do not need to get a kill with ALL the ammo types in one glide. You can get one kill with each type over multiple glides.
This isn't my video and full credit goes to the maker of this video, but it serves as a good visual guide as to what the achievement requires