The key to my mountain shooting success can be summed up in one word — practice.
I know, not real cutting edge. But the bottom line is, if you're going to bowhunt the backcountry of the West effectively, it takes commitment. I shoot virtually every day except during the months of December and January. I'm always on the road attending shows then so I consider that time period my "off-season."
Shooting every day sounds overwhelming, but it really isn't when you consider that on many of those days I may shoot only a couple dozen arrows. That takes only about 15 minutes and for most of these quickie sessions I shoot at 20 yards. I'd venture to guess each one of us has an extra 15 minutes a day to dedicate to our craft.
Accurate shooting is all about consistency, which means aiming and using the same form to hit the spot at 20 yards as at 60 yards. I supplement my short practice sessions with longer outings, too. A couple times a week I'll go down to the local pro shop and shoot against my buddies or shoot in one of the indoor leagues. One evening a week I'll shoot at my friend's house where we stretch the shot distance to longer yardages. Long-range practice exposes errors in form and equipment, and I find it very beneficial. Most years, I will also shoot about 10 3-D shoots.
I hunt the rugged, up-and-down country of the West a lot, and I've found a bubble level on my sight is a must. Not a cheap bubble level thrown on for looks but a quality bubble. I use a Spot-Hogg sight that features a precision bubble but also has 3rd axis adjustment capability. If your 3rd axis is set correctly, at full draw, your bubble will indicate when your bow is perpendicular to the world no matter what angle you're shooting at. This is crucial when shooting uphill or downhill. If your bubble is lying to you, it's highly likely you'll miss, or worse.
Another thing my sight has that helps prevent canting is a vertical wire aligned with the pins. I've found I instinctively keep my bow more straight up and down with a wire than without.
The most important thing is to include uphill and downhill shots in your practice regimen. Use a rangefinder that features angle compensation and become familiar with how angles affect the yardage you must shoot for. Also, practice shooting from your knees, and from a sitting position while making sure your bottom limb clears the ground. Pay attention to the details because in the mountains, the little things always count big.
Finally, avoid cramming your weekly practice sessions into one or two days. If you shoot for an hour or two at a time, most of that practice will actually be reinforcing bad habits or improper shooting form due to muscle fatigue. That can be hard on your mental confidence as well.
You've heard the old saying, "Perfect practice makes perfect." Well, that couldn't be truer than it is for shooting a bow and arrow. Short, high-quality practice sessions, in which you're focused on pinpoint accuracy, will pay huge dividends in the mountains. Good luck.