The Third Spot
The old-school book says to put your best high-average hitter here. The lead-off hitter should already be in scoring position and a hit drives him in. Wham, bam, thank you ma'am.
The Book says the #3 hitter comes to the plate with, on average, fewer runners on base than the #4 or #5 hitters. So why focus on putting a guy who can knock in runs in the #3 spot, when the two spots after him can benefit from it more? Surprisingly, because he comes to bat so often with two outs and no runners on base, the #3 hitter isn't nearly as important as we think. This is a spot to fill after more important spots are taken care of.