A sling is more than just a strap to carry the rifle. Properly using a sling can provide a sturdy shooting platform.
I prefer a Ron Brown 1907 sling. While slower to sling up, I feel more stable with a 1907 over a web sling.
The sling pictures is a John Weller 1907 I picked up at Camp Perry a couple years ago. Sadly John passed away since then and these slings are no longer made. Ron Brown slings, sold by Creedmoor sports are the best slings on the market. They are thicker more sturdy and stretch less than most other slings.
First you will need to have your 1907 installed correctly. CMP has a detailed write up on this below that can help get you started. However, they do it wrong. Put the frogs facing in towards the rifle. As you’ll see below this will put the frog on the top when slinging up which is easier to manage and less likly to slip.
Once the sling is set up correctly remove the frog on the short strap (aka tail) of the sling from the looped long strap. Then pull it free from the rear sling swivel.
Adjust the sling so there is a large enough loop to fit your arm in. Pull the upper keeper away from the frog so that it is easier to adjust.
Turn the loop clockwise so that the loop faces you. The frog should be facing more or less to the left or away from the rifle. Be careful not to do this step twice in haste and get the sling twisted.
Then stick your support arm through the loop.
Push the sling up your arm as far as it will go. There is some amount personal preference here. The key is to do it the same every time. I use the pad on my jacket as a reference point.
Once you have the sling all the way up draw it as tight as you can. I do this by pulling on the lower half of the loop with my left hand and holding the upper half of the loop with my right hand.
Once the sling is nice and tight, slide the upper keeper all the way down to the frog which will lock it all together.
Then you are ready to go. Place your support hand over the sling and grip the stock.
You will need to determine what the best length and support hand position Is for you. Rig up, get into position and dry fire a few times until you feel comfortable.
My left handed wife informs me I should add that this depicts a right handed shooter.