On any hit into the gaps or down the lines with a runner at first and the outfielders are unable to cut it off, your first thought is to try and stop the runner from first from scoring. If the runner has average or better speed, this can be difficult to do. As you work on this play during practice make sure you use a runner at home and first and give the defense opportunities to make plays on both runners. Many times your team will have a better opportunity of throwing out the trailing runner at third than getting the lead runner at home.
I have the shortstop or second baseman as the fielder going out and becoming the first person in the relay. The other infielder should line up about 10 yards behind the first infielder. I've seen many double cuts where the infielders are standing about 5 feet away from each other. That doesn't do much of anything. The infielders need to be spaced so together they can cover the most space on the throw coming in.
The diagrams below show how I position the defense for this play.
On any hit to left of left center, the first baseman has the important role of trailing the hitter to second base. If the runner stops between second and third the first baseman has to be in position to get a throw at second either from the cutoff or in a run down situation.