The left fielder gives way only to the center fielder on balls they can get to. They should go toward the infield calling loudly for the ball if they can catch it. They should go quietly toward the center fielder.
The three rules of defense apply to the left fielder like everybody else. This means the left fielder will have to do a lot of running.
The left fielder should back up second on hits to right field unless the center fielder comes over to back up the base, then the left fielder hurries over to back up third.
On hits to center the left fielder goes over to help.
On throws in the infield, the left fielder backups up third. This is especially important when the catcher throws to third since if the ball is thrown by third base a run will score unless the left fielder is there to catch it.
On bunts, the left fielder backs up third and covers third if the shortstop does not get there in time.
The left fielder should make all throws low enough for any player between the left fielder and the base they are throwing to to catch. If the left fielder catches the ball where they stand or coming in toward the infield they should throw directly to the base. If they must go back to get the ball they should throw to the relay man.
Throws must be low. This cannot be emphasised too much. All the time the ball spends going up and down the runners are running. When catching fly balls in practice the outfielders should make low throws back to the person hitting the flies even if this means putting a relay man in between. There should be no high throws at all in practice by anybody.