...lots of good advice here.. I want to add my thoughts... I think that shooting at an animal can be an un-nerving experience, if you are an ethical hunter...you are wanting to kill the animal quickly and cleanly, and are subconciously afraid of messing up... at least I was that way, starting out. I believe there are two things you can do to eliminate that nervousness.
1) Practice. Shoot your rifle enough off sandbags to know its accuracy potential. Then practice standing... leaning on stuff, as you would in the field.. sometimes point of impact is different when using something other than sandbags. The point is, practice enough that you have NO doubts that the bullet is going where you intend for it to go. NO doubts.... that gives confidence.
2) Mentally rehearse what you would do in any given hunting scenario. When sitting in your blind, be thinking.. "Ok, if a deer comes out around that bush, when would I shoot?" or, "if the deer were standing facing slightly away from me, where would I aim?"... just go through all the "what-if" scenarios you can think of. If you do it (shoot the deer) mentally time after time, then you will not be flustered when the actual time comes... you will have already done it many times... mental preparation works...

"Progress, far from consisting in change, depends on retentiveness..those who cannot remember the past are condemned to repeat it." Santayana