I always arrive at the field knowing what i want to work on. I don't show up and not have a plan. Showing up and winging it may work sometimes in a crunch but more often than not you will draw a blank on what to do and you loose the attention of the players and the confidence of the parents.
Pick out three skills you wants them to learn right away. Work on the one that is most important they master right away. Then go to a different skill of equal importance. The last one you touch on it and send them home told to work on the third item. Younger teams have to keep moving or they just get bored.