Not sure if this will help or not, and I am not sure I can even explain exactly what I try to do but here goes.
As I bring the bow to full draw I try to pretend I am trying to hold a softball between my shoulder blades using my back muscles. As I release I try to make the release as much a part of contracting my back muscles as it is "letting go of the string". Is really harder to explain that it is to do. For all I know this is bad habit/form but it was how I taught myself to release when I was shooting wheelies with a realease and it made sense to me to use the same technique (modified of course) when I went back to shooting fingers.
Those more practiced than myself please comment as I would really like to know if this is bad practice myself.
So far as axcercises. I have some basic ones that I do at least 3 times a week, more often if I am trying to adjust to an increase in weight. As with any excercises work into these slowly to avoid any further injury.
1 - Using a bow that you are comfortable drawing bring the bow to 1/3 your draw length and hold while counting to 3, then bring to 1/2 draw and count to 3, then to your anchor and count to 3, now reverse this while letting the bow down stopping at 1/2 and 1/3 draw. Repeat this with your left arm as well. Do 3 to 5 sets. If I am trying to increase draw weight I hold each for a 10 count instead of 3.
2 - Bring the bow to full draw and anchor in a rapid, but smooth manner, then once at anchor slowly let down the bow while counting to 10. Again, if trying to increase weight I count to 20. The negative resistance does a lot to build strength because it is the opposite of what you are consistently doing while shooting.
3 - Dumbell Rows are great. Do these with enough weight to provide adequate resistance, not so much that you injur yourself. When doing rows using a count method is a good way to avoid just "going through the motion. Count to 10 when lifting the weight, count to 5 while holding at top of the stroke and then count to 10 while lowering the weights. If you can't do this at least 5 reps then you are using too much weight.
One last note. I have some issues with my joints as well. Too many crazy stunts when I was younger are catching up on me. I have found Ostio-bi-plex to be a blessing. It isn't cheap and I keep meaning to look for a cheaper alternative but for me this stuff does wonders!
Truly hope this helps!