This tip is a very good conditioning drill that will allow your player to develop physically.
Take the players to the foul pole in left or right field, time them from foul pole to foul pole to get a base time. Then have a set time that they should complete each of the laps. I use 7 laps because of the number of innings we play. I require that all team members finish under the time required to make the lap count.
For me this helps toughen my players for game and competion.