I like to go with a counter-clockwise route for all my farm maps. I go up the eastern side, turn left, and go down the western side. This route works for the rectangular farm maps common to Unai and Harvey Maylor, but Television's maps a little less conventional. Some of Unai's maps have twists and turns as well.
Whatever method you settle on, stick with it and use it consistently. Find a route that minimizes overlap and works you back near the map entrance when you finish your last spawn. This is not only efficient, but it helps you avoid accidentally completing a mission you do not want to complete (particularly important in missions where the objective is to kill everyone on the map).