You can either adjust the grind to be slightly more coarse and pull faster through the grinds, so you end up with less of an extracted shot, or you can use a finer grind and then choke the machine out and cut the shot. I usually do the latter myself.
Adjust the grind so it chokes the machine, then back off one or two clicks on your grinder (or whatever adjustment you have). Then use a light tamp (since the finer grind will slow the water down on its own). Then lift the lever and do a 5 to 10 second pre-infusion. I start the pull, until you see the droplets forming and trying to join into a stream. Then pause and back off on the pressure. Then continue forward. At this point, sometimes I cut the first second or two of the shot, then pull for about 10 to 15 seconds and get as much as you can out.
You'll end up with a short / concentrated shot.
The first method (a fast, brief pull through coarser grinds) will give you a short shot, but it will be more in-line with a normal shot, just less volume.
Those are the two methods I have used.
A good method for testing is to use the 2nd method above and cut the shot (5 seconds at a time) across 5 shot glasses. Then test each one and see which flavor profile you enjoy best. That is always an interesting test to do

Ray