I like to place stands on the south or east side of a trail because the normal prevailing wind is northwest. But as stated above, avoid those stands when the wind will send your scent in the direction you expect the deer to be coming from. Multiple stands set up specifically for various wind direction are helpful, as well as mobile setups like climbers. It is also helpful to Check out how obstacles will effect wind direction. A west wind coming over the tree tops will often roll back eastward as it drops into a field or a ravine. A scent smoker has become a popular means of "hiding" your scent, making wind direction less of a factor.