Every good deer hunter constantly monitors the wind direction. You always want to keep the wind in your face so that your scent isn't carried downwind alerting deer of your presence.
Besides just wind direction, you should also be aware of thermals. Thermals are a weather related phenomenom related to rapid temperature changes. When air heats up rapidly, as in the morning, it becomes lighter. Conversely, when air cools quickly, it becomes heavier. The warming morning tends to drift uphill, while the cooling evening air falls downhill.
Remember that when you are planning to still hunt. In the morning, hunt downhill, and in the evening, hunt uphill. That way the thermal activity will keep the air blowing across your face away from the direction you are heading, and out of the nose of any deer ahead.