As you are aware there is no good tutorial or manaual to explain everything to new players. Post here hints what people can do - what they should do - that isn't obvious enough, something you discovered or know that can come in handy.
- Contrary to common belief squad leader and commander doesn't need binoculars to mark target for artillery. I am often good without binoculars. They are, however, very useful when you stand in relatively safe distance and SPOT targets like tanks, groups of enemies with "Z" key, it works almost like recon plane, but isn't global since you need to spot each enemy on your own. Even common soldier can spot. If you spot a tank and then mark artillery on him sensible commander should know to place mortar on him before it moves away. It's way better than putting artilley mark and writing things on text chat and when in doubt it helps to tell friend from foe.
- You can give machine gunner ammo when he is undeployed. Press "ctrl" near him to do that (I am not sure if it works when he is deployed). Now instead od 3 mags he has 5 to cover advance/defense and you get XP for doing that.
- Machine gunner can press "C" to crouch to change his mag. That way you don't stick your head out while reloading and being defenseless.
- You can use "Q" and "E" keys to look out from the corners you CAN'T use as cover. But you might know that. Also you can use same keys while proning to not expose yourself needlessly (you can't "Q" and "E" while being prone as machine gunner).
- While being under cover (ctrl key) you can see shield of different colours. Green is solid and is good as cover. Red only conceal you from the enemy and shoot through it will most likely to kill you. Any explosion will obliterate red cover. Use it for concealment only. Yellow needs to be confirmed.