This Guide/Tutorial helps both experienced and begginer players. Also this is my first guide so I am sorry if my format is wrong :D (Sorry for bad english)

1. When you grapple an enemy (e) you can press 'ctrl' to put them in a position like you taccled the enemy from running.
2. If you are crouching in the open world and come across a standing npc you can 1 tap them with 'f' or 'left mouse click'
3. If you are at a saloon with a huge window (e.g.:Valentine) and you grapple an enemy there and put it in a position where it's shoulder is touching the window and you hold 'a' or 'd' (depending on wich shoulder it's facing, so if the npc's left shoulder is tuching the window you have to hold 'a') plus keep pressing the 'f' button you can throw the npc out of the window like how tommy threw arthur out the window.
Here is a visual tutorial: https://www.youtube.com/watch?v=Ad1x_INfhAo

4. If you grapple/taccle a witness and you hold 'e' in stead of pressing it you will choke it instead of sliencing it.
5. If you are in a fight against many people (e.g.: the workers in St. Denis) you can pull out your knife or machete to kill them faster (NO OTHER MELEE WEAPONS WORK)
6. Also with unique keycombinations you can make special knife kill animations which aren't promted as takedowns (e.g.: kicking knee cap and stab in neck).
7. You can stealth kill people who are on a horse (they have to be stationery)
8.. You can also do silent melee takedowns with bows, throwing knifes, tamahowks ect.

I hope this guide helped both new and experienced players. Have a blessed day:D