I always do a location scout before a wedding or a portrait shoot. I usually do this at the same time of day and year that the shoot will happen so I can assess the light and explore. I hate being unprepared and I like to think about interesting ideas before arriving on assignment day. I always carry a notebook around with me when doing location scouts so I can jot down ideas.
If it is a destination wedding I will always arrive the day before the wedding so I can check out the venue and the area around the wedding.