Easy "A New Master" achievement

To be able to Brand a Captain while in combat, you must first complete the "Queen Of The Shore" story mission, and buy the "Combat Drain" ability. Completing that mission will unlock the Brand ability, and buying the "Combat Drain" ability allows you to Brand enemies during combat, without having to grab them. Captains spawn randomly all over the map. Drain a Captain's health until the skull symbol turns green, then use the Combat Drain finisher several times to Brand a Captain and get the "A New Master" achievement.

Easy "Black Celebration" achievement

First, successfully complete "The Outcasts" (early) story mission to obtain the Poison ability. Then, go to a Feast. Feasts randomly appear on your map and are marked with a red icon. If no Feast is available, scroll over a Forge Tower on your map, and advance the time to make new events spawn. Do this until a Feast appears. There are multiple drinking bowls at each Feast. The Captain will walk from one bowl to the next. You must poison one of them without being seen and wait for the Captain to drink from it to get the "Black Celebration" achievement. If you are detected, you must quit the game to try the event again.

Easy "Height Of Despair" achievement

A great area to use Strike From Above while at least 60 feet above your target is at the eastern most Forge Tower of Udûn (the map where the game starts). There are a couple of enemies roaming the area. Attract one Uruk, then lure the Uruk all the way to the tower, climb up, and perform a Stealth Takedown from above to get the "Height Of Despair" achievement. The Uruk may not be in combat mode while doing this. You must stay undetected, or else you will only knock the Uruk down instead of performing a stealth kill.

Easy "Iron Of Death" achievement

To issue a Death Threat, you must first buy the "Death Threat" ability. Then, dominate any enemy desired, and issue a Death Threat. Mark the Uruk you have chosen, hunt him down, and kill him to get the "Iron Of Death" achievement.

Easy "No Power In Numbers" achievement

First, play until the end of the story when you get the ability to command Uruks. You need to brand a Captain and command him to infiltrate a Warchief. However, this does not always unlock a recruitment mission, as it is a random type of mission. Thus, keep commanding Captains until a recruitment mission appears on your map. Once you start a recruitment mission, defend your captain and kill other Uruks. After successfully completing the mission, kill your Captain and all his recruits to get the "No Power In Numbers" achievement.