If you've never used a rifle sling when elk hunting, it's time to consider the benefits. Long, heavy guns are great for elk hunting, giving you the power and accuracy necessary to bring down big game. But they're also heavy and awkward, and they can be a huge hassle to carry, handle and to steady for a shot. This is where a rifle sling comes in - slings make it easier to carry a rifle or shotgun, and can help you in accurate sighting when there's nothing to use as a rest. But they do have the drawbacks.
For starters, like anything else that hangs off your gun, they can get in the way. If you're sitting on the ground for a long period and won't be needing the sling, then remove it. You may also want to take it off if you're in a heavily wooded area so it doesn't get caught on a branch. Having something dangling from your gun is rarely a good idea if you're trying to be stealthy and not draw attention to yourself.
Simple slings are best, and just a black nylon strap sling works great with lighter-weight rifles. For heavier rifles more commonly used when elk hunting, a larger padded sling may be your best bet. There are a variety of brands on the market, some very good and some pretty bad - try out a sling with your usual elk rifle before buying, so you know how comfortable it feels.
You'll often see hunters sling their guns over their shoulders, essentially carrying them behind them, on their backs. If you're very tired at the end of a long day of hunting you may want to do this, but otherwise you should keep your elk in front where you can grab it at a moment's notice - you never know when that big buck might come along! Shoulder the sling with the gun in front of you, so that it can be shouldered when you wanted it. If you're right handed, try wearing the gun this way on your left shoulder - that way, you can reach for the grip with your right hand as you slide the strap off your shoulder, and pull the rifle straight up to sight it.
A rifle sling can also help your accuracy, which is a real bonus when elk hunting with a large, heavy gun. If there's nowhere to rest your rifle, you can wedge you off-side arm into the sling to steady. Just make sure you practice shooting while wearing your rifle-sling before elk hunting - after all, practicing your shooting is fun, and it'll prepare you for any situation in the field.