A short tip…
If you are actively engaged and are moving up to a position of cover, get your weapon up and on target before you arrive. Many people run up to a barricade with their weapon in a depressed position and waste time and movement repositioning their firearm and finding their sights once they get there.
What you want to do is get your weapon up on target just before you arrive, this gets your target acquisition process on-line that much faster.
While this may seem a bit pedantic, I find it illustrates a mindset of smoothness and economy of movement that will serve you well.