In What You Need to Know About Rifle Slings, we talked about carrying your rifle, and how to use the sling to get steadier.  

In the comments section, Misreading The River and Paul noted about shooting after carrying all day long, or under stress. In this article, I would like to address some exercises that while may not be actual combat, but give you an idea and how to train to shoot under pressure along with some additional exercises both physical and marksmanship.

Pressure
The infamous SHTF Mr. Mutant Zombie Biker (or MZB) is not just going to let you roll out your shooting mat, set up your bi-pod rifle, set rear bags and then stand perfectly still while you take a shot from the prone at him at 100yrds.  

More like,

"AAAARRRRR! AAARRRR!"

And then rush you with his AR15 with the under rail mounted chainsaw, buzzing at full tilt while you roll out your mat. We all know how that ends in a 1980s style horror/slasher flick. That, and don't go down into the dark basement to investigate that really creepy sound unarmed.

As I mention in How to Become a Good Shot, there are different competitions you can compete in to become a better shot.