I used to be pretty good at this game hmmm some tips:
Learn how to master the other specialties.
I mouse hotkey the 3rd and 5th weapon points. so a quick click of the mouse will bring up the shots to heal and another click returns me quickly to my rifle. any other specialty i use the wheel to scroll from the 5th weapon point to get what i want i.e. click to drop ammo scroll up one to toss a flare for an air bombing.
One of the neatest tricks with signals is to press "B" to bring up binoculars then click with your mouse and this will call mortars on the position you clicked on. When I'm signals this is often the last thing I do when I find a pack of enemies and realize I'm toast (ahh revenge, so are they )
one of the funnest positions in the game I love stealing uniforms to go under cover then planting backpack charges (hotkey click, scroll up one) or sniping targets from afar.