Ablebonus: it took some work and everybody has a different time-frame but paying careful attention to my form was huge. Keep in mind there are folks on this form that could out shoot me blindfolded at 50 yds! But, here are, in order, the things I did:
1. Get a bow I like and was comfortable with (weight, riser, & grip)
2. Tuned arrows to the bow so that I could rule out my tackle and focus on me
3. Shoot everyday with a purpose and put it down as soon as form fails. 4-5 shots at a time. Forcing myself to slow down.
4. Each day I tried to look at each phase of my shot (aim (pick a spot), draw, anchor, release, follow-through)
5. KEY OBSERVATION: I noticed that I tensed before I came up to draw. The tension was anticipation of the weight of the bow and that translated into mental tension for the shot SO... I began dropping my shoulders and releasing tension as a pre-draw cycle in my draw cycle sequence. This is something I started doing with compound shooting and never realized I did it with the longbow.
6. Mental practice. I shoot in my head before bed and when I put my son to sleep. Sounds silly, but it helps. A lot. See Jay Kidwell's book on Target Panic for more on that... but every archery coach I've read recommends this.
Hope that helps out some... take what seems useful... and keep at it!