like others said if you don't get the fever its time to quit...

but what I do is close my eyes for a few seconds. and above all don't move when you first get the adrenaline rush...because that will make you make mistakes...try to calm yourself down and let the rush subside a little. Once your heart rate is back down a little then you can make your move on the deer...if it looks at you STOP don't move to the best of your ability till it looks away and starts moving again. Wait to draw or position your rifle while the deer is walking behind a tree...then stop him/her when you are in a good position to shoot the deer in the vitals...