Typically during the beginning of the season, most deer are moving around slowly or grazing slowly because they are not pressured by the rut yet, and also because they may not know you are there yet. But as more hunters start making noise or leaving scent in the woods, you will start to see the deer change their habits and start looking and smelling for danger more often. Finally, when the rut comes into full swing, you will see the bucks on a steady trot looking for doe's. They are not going stop and be patient for you while you try to nock your arrow. Therefore again I emphasize the importance of timing and understanding your environment.
Practice is always the key.
It holds true for every sporting event ever held, whether it is basketball, football or archery. No number one college or pro basketball team ever won a championship by only shooting freethrows, they had to practice in scenarios that were as realistic as possible to find out how to shoot the ball while being defended. The last idea in practicing in your environment is aimed more towards the treestand archers. If you normally use a treestand, you will need to practice in a sitting down position. I personally enjoy the use of a treestand since it allows me to get a wide field of view.