Check out how you can attain easy and secret achievements in the Batman Arkham Origins game:
In one of the first missions of the game where you need to track down the Penguin on his ship, you will encounter Tracey (Penguin's assistant) and her goons. You will then reach the first predator room of the game. Crouch and sneak up to an isolated enemy and perform a silent takedown. Repeat this to six enemies inside the room unnoticed to get to the "Silent Knight" and "Anyone See That?" achievements. If you have passed this stage, there are a lot more opportunities to do so but ensure you do this before you complete the story because the enemies will not respawn after completing a predator room.
Reach a x50 combo easily in "Intensive Training," the first combat challenge. Enemies do not have shields or armors in this challenge. Reach Round 4 to have enough enemies that can build you up a x50 combo. Make sure you don't get hit while fighting by performing a standard strike then jumping over an enemy. Repeat this. Enemies will not be able to hit you but it is safer and easier even if it takes a bit longer than fighting and countering the normal way. Never perform any combo finishers or attacks to keep the enemies alive longer. If Shock Gloves is already unlocked, activate them to get a x2 multiplier with every hit.
Early in the game, you will fight against Deathstroke on a story mission. When he attacks you need to counter him. Attack Deathstroke using Batman's normal strike. This may initiate a QTE where you have to press the counter-button once it is displayed on screen. Don't press the button too early or too late because your counter attack will fail and Deathstroke will be able to hit you. If you get hit, pause the game and key in the restart button. The fight will start from the beginning and you can retry. You may miss the Deathstroke fight and if you do, start a new game and play until you reach the Deathstroke Boss fight where you can get the Point Counter-Point achievement.
Here's a list of the secret achievements you can discover in the Batman Arkham Origins game:
City of Assassins (10 points): Identify Black Mask's assassins.
One eye open (15 points): Defeat Deathstroke.
Nobody that matters (15 points): Who is the Joker?
Everyone wears masks (15 points): Find the Black Mask.
One Rule (25 points): Save a life.
Perhaps sooner, Perhaps later (30 points): Defeat the Joker.