Following Buitenzorg's last comments, knowing the wind is the trickiest part. If there is no smoke or other indicators, you have no choice but to use the wind at your departure point.
There is a small site I occasionally go into - actually the back car park of a local pub. The pub is at the front, and there are buildings set back on each side so there is only one way in or out directly from the back of the site. This is over open fields which drop away quite sharply, so the approach and departure track are OK. However I won't go there unless there is no wind at all, as if there is you have to either land or depart with the wind behind you.
A question for the experts. Faced with this situation, obviously the best answer is don't go there at all if there is any wind. But if you are faced with a site with one single entry and exit path, would you prefer a small amount of wind behind you on approach, take off or at 90 degrees?