Not trying to be a smart-ass but..... practice, practice, practice. To be more succinct. Practice from a tree stand shooting down, practice from a draw where the deer is above you, practice with your heavy coat on and with and without gloves, and understand that on your first few deer sitings, you will be extremely nervous and excited. I think we all miss our first one or two.
Feel lucky you got that close to one, good luck, and GOOD HUNTING!