Know your limits with your bow. Forty yards is a long shot with any bow for any hunter. If you are not sure you can make the shot then don't take it! Drawing down on an animal with uncertainties will only make things worse. Step off a few yardage ground markers before you climb into your stand. This will eliminate all the 'trig & calculus' distance calculations that are spawned in your head when a giant buck steps into sight. A combination of being nervous and that small doubt of shooting at a long distance will cause you to miss even before you let the arrow fly.

Make sure that your are comfortable while hunting. Being cold (or hot) while hunting will also add to the problem. Don't wear clothes that are to tight or too loose. Remember, you're not going on a date and the deer don't care what you look like. Dress correctly according to the conditions in which you are hunting.

Position your tree stand correctly. Some hunters will tell you, "The higher, the better". Well, not if you are afraid of heights. Granted placing a stand high in a tree will slim the chances of animals seeing you or smelling you, but there are other alternatives. Find out which way the wind usually blows and watch (or listen to) the weather report. Find a tree that has some cover that doesn't leave an outline of you against the sky. Keeping these few things in mind will help you when hanging a stand that isn't 30 feet off the ground.

Never take untested gear hunting. I think this one is self explanatory. Just think what it would be like to be sitting in your stand and all of the sudden, out of the corner of your eye at 50 yards you see, walking away, a 160-class, 10-point buck. You know the bucks are rutting hard and heavy. You pull out your brand new grunt call, that you purchased the night before, and you have just realized that you have never gave it a try. I'll not say anymore about it.

Practice with a "surprise" release!  This type of release will teach you to be patient very quickly.  Try a Zenith back-tension or a SCAT JS.  The SCAT JS works very well if you are a caliper style release shooter.

Workout your shoulders with light free weights.

Crank your bow back a little bit, five pounds or so. You may have your bow set to high for you to handle.

Don't hold your breath while in full draw.  Breath!

Don't use practice targets with the colored circles/dots. Use animal replication targets when possible. If using a bale of hay or an arrow pillow for a target, use a very small zero-point marker instead of a larger one -- about the size of a half-dollar.

Move your bow into range in the opposite direction that you have a problem with. Example: If you have a problem of shooting too low, then start with your sights at the top of the target and move your bow down into range.

Make sure your bow's draw length fits your draw length.  If your bow doesn't fit you it will be uncomfortable, which makes you want to pull the trigger quicker.  Trigger punch!

When the panic attack hits you while at full draw, let your bow down without firing.  This will secretly teach you that you have full control over your bow, and not your target panic.

Practice drawing and aiming at a target without actually shooting the arrow.  Hold on your target for a few seconds and then let your bow down.  Repeat several times. This will also teach patients and that you have full control over of when to shoot.

In conclusion. Lots of practice. This is the full proof solution. I strongly recommend investing in a "surprise" type release.