I want to make a ristretto. Besides grinding my coffee finer, do I need to increase the pressure of the steam, or should I leave it the same?
Typically, a ristretto is an espresso shot pulled with half as much water. If you assume a normal shot is 30ml, the only practical difference in pulling a ristretto is to stop the extraction at 15ml.
The coffee grind, quantity and pull pressure should remain the same.
Regardless, if you feel as if the shot is taking too long, or coming out too fast, you could try adjusting the grind before adjusting the pressure, which should be trickier.