A rifle sling is considered by many, one of the most important tools available to assist with accuracy. If used properly, it can assist with stabilizing the rifle in the standing, seated, and prone positions. I would highly encourage you to check out the Project Appleseed website and consider attending an event. The lessons learned will definitely help your marksmanship and one of first lessons learned is the proper use of the rifle sling.
You can also do a search on INGO and find many threads about Appleseed and the lessons taught by their instructors.
Using a sling will help stablize your shooting from any position, I recomend you get one of the quick adjusting nylon slings, the width should be over 1" and extended you should be able to shove your left arm through and wrap your left wrist around and grab the forarm of the stock, as you pull it up to shooting position it should be tight enough to stablize your rifle. Of course there are several ways to use it, but they all should wind up holding the rifle up tight, when in shooting position. The method I outlined is called or used to years ago, the hasty sling. I have used it for over 60 years.
Bill...