The best way to train for shooting a bow is by shooting a bow. Being in good shape is important but archery muscles are developed by shooting a bow. If you are shaking when drawing a 45# bow going to 60# could cause injuries. How often do you shoot and how many arrows during a session? One good training method I used when I started shooting(this was with a compound) was to slowly and purposefully draw the bow to my anchor, hold for 10 seconds and slowly let down. I would do this 10 times then rest. A bit later I'd do it again. When I started, my compound was too heavy for me but I wanted to be able to draw it to anchor with the least possible movement. By hunting season I could draw my bow to anchor, standing or sitting with very little other movement. I know holding a selfbow for 10 seconds is a no no so slowly draw to anchor, hold for 2 seconds, concentrating of a spot then slowly let down. Do this 10 times and rest. Also, and this is important because some folks I've known can't let down but release from full draw, do this without an arrow on the bow, just in case.
When you do step up to the target butt concentrate on your target, not just the target but the spot where the arrow WILL hit. With an arrow on the bow draw, anchor and release always concentration on that spot. Go retrieve that arrow and do it again and again, etc. Start out at 10 yards and do this 10 times then walk away and come back later. When you are consistent at 10 yards move to 15 yards.
When I shoot now I pick my spot, draw to anchor and release as soon as I hit anchor always concentration on the spot where the arrow WILL go, not where it should go but where it WILL go. If I find myself short drawing I will hold for a second or 2 before releasing. This helps me concentrate on my form, a good anchor and a clean release then I'm back to my normal shooting style.
45# is plenty enough weight to hunt with. You have to develop good form, good anchor, good concentration and good muscle memory. When I'm shooting I don't want to think about anything but where the arrow WILL go. Not form, not anchor, I don't want to even be aware of my bow or arrow. I don't want to think about ANYTHING but hitting that spot, and that takes your full concentration.
Back in 1999 I bought a new glass lam longbow from Mike Treadway. The first year I had that bow I calculated I put 10,000 arrows through it. I was shooting 100 arrows a day for most of that year and I was trying to concentrating on each shot, my form, my anchor and my release. This helped me with the muscle memory and once I was comfortable with that I only shot a dozen or 2 thoughtful shots a day. A month before hunting season I would only shoot one arrow a session. That was either in the early morning or late evening when most hunting shots happened. I also shot from an elevated stand(my front porch) at my comfortable height and shooting range(from a few feet out to about 25 yards). Believe it or not those closest shots were the hardest.
And one more thing to end this epistle...if you are tired, aggravated, mad, frustrated or for any reason you can't concentrate, put the bow down and walk away. Bad habits are very hard to get rid of but very easy to obtain.