My advice for story mode:
- If it's your first playthrough I think you should try and play it on hard mode at least
- Take your time, don't rush
- Use stealth and try to sneak around as often as possible
- Take time to explore and collect things like notes and items
- Read the notes/letters, don't ignore them
- Conserve ammo as much as possible
Advice for Factions (MP):
- Don't sprint around like it's COD
- Revive downed team mates when it's safe, don't ignore them unless it's absolutely necessary eg. if there's a choice between reviving and getting a special execution, then your revive your team mate!
- If a team mate is healing you, then let them heal you, you'll get heals and your team mate will get points
- Don't go into your backpack unless you're in cover or you're absolutely sure nobody can see you
- When going to a supply box make sure you pick up all the items, I see a lot of people who walk over the items and accidently only pick up a few things because they can't see the rest. eg: they could've crafted a nail bomb instead of a smoke bomb if they picked up all the supplies.
- smoke bombs are very effective and underrated. they stun the enemy, provide a screen (protect against snipers), a distraction and it's also a way to get the enemy to run away (they might think someone is coming to shiv them)