I assume your problem is you aren't seeing deer. If you see deer but they are too far away, you need to set-up closer. If you shoot at deer but miss, you need to practice shooting at the rifle range. These are pretty obvious, so I assume your problem lies elsewhere -- that you aren't seeing deer.
You must hunt where deer are. Before the season scout your hunting ground looking for deer sign. Look for deer hair on fences where deer may cross fencelines -- either crawling under or jumping over. Look for deer tracks, particularly after substantial rain. Look around ponds and creeks for deer tracks. Look for deer poop. If you see no sign of deer, your hunting ground may be bad.
Assuming you have found indications that deer frequent your hunting ground, you need to figure out the general behavior of your deer. Others are more expert than I, but I can provide you some high level insights into this and leave the more sophisticated details to more veteran deer hunters.
Deer are a prey species. Other animals want to eat deer, and deer want to avoid being eaten. This explains much of deer behavior. Deer want to stay out of sight. They fear being eaten and avoid behaviors which raise their exposure above a flexible comfort threshold. Typically, deer eat in low light conditions when they feel less vulnerable to attack and hide during daylight hours, lieing on beds where they spit up and chew their cud. Deer often move from feeding areas to bedding areas at first morning light and from bedding areas to feeding areas at last evening light. If hunter pressure is heavy, the deer may move before first light and after last light, making them very difficult to ambush. Also, a full moon may result in the deer doing their movements at different hours and being out of sight during all daylight hours. So, your best bet is to be in a stand overlooking a trail between feeding and bedding areas at first light and last light. Once you have determined deer are present in your hunting ground, you want to figure out where the deer are going to eat and where they are going to bed. Bedding grounds are often on the sides of hills (during the day, thermal wind currents go up hill, carrying the scent of predators to the deer) in brush or high grass or weeds, perhaps on the border of thicker cover that they can escape to in emergencies. Feeding areas are where you find food -- acorns, apples, persimmons, etc. You also should know where water sources are. Figure out where the deer move, by looking for trails and footprints. Remember as deer move from one area to another they like to have enough cover to be comfortable. They won't take the densist, nastiest path -- because this will be harder, and deer are lazy just like us -- but they will follow a trail that offers enough cover that they feel comfortable. This is a relative thing.
Look for low creek banks or shallow spots in creeks where it is easy to cross. Look for "deer funnels" -- features of the land and cover that tend to encourage the deer to travel from point A to point B following this specific path. For example, a narrow band of trees between a bedding area and a feeding area is likely to be a deer funnel, because a deer moving from one place to the other will avoid walking across open fields if there is a bit of cover they can follow instead. A depression such as a shallow ditch may be a funnel because it may provide a sense of security and comfort to the deer when travelling through it versus walking open ground. Set-up your ambush overlooking these deer funnels from a distance at which you feel comfortable shooting. Too close makes it easier for the deer to detect your presence; too far makes the shot difficult or places obstructions in your firing lane.
Deer have very good senses. You don't want them to smell you. Make sure the wind is NOT blowing from you to the deer, or you will never see them. The wind is preferably blowing from the deer to you or crosswind to you and the deer. Deer also see well. Try to place yourself where there is cover behind you -- a bush, a hill. It is very easy to spot you if your silouette is visible against the sky above a hill. If you can place yourself in shadow, this helps keep you hidden. If you can conceal parts of your body behind brush or other obstructions, this helps conceal any fidgity movement of these hidden parts -- such as shifting legs, etc. Try to move as little as possible, and when you must move, move slowly. If possible, wear some covering over your face. Human skin "flashes" as the head turns and light is reflected more or less in the direction of the deer. If possible, obscure your eyes, as humans have eyes dispossed as predators (eyes directed forwards). If a deer looks at you, avoid returning the deer's gaze. When a deer is looking at you, don't move. Wait until the deer's eyes are averted to move, for example to raise your rifle to your shoulder. Avoid unnatural noises like velcro fasteners unfastening, metal zippers jingling, nylon brushing on bushes.
Others can provide other details.
