It should be lighter pressure for thinner fabrics or those with nap to prevent marring, and greater for heavier fabrics so they feed well. It is probably a good idea to test the pressure with some scraps before you start your project. Fabric should feed without puckering (too much pressure) yet be held securely. Turn the pressure knob on top clockwise to increase and counterclockwise to decrease, usually. My Pfaff 1473 pressure increases by pushing downward in increments.
I hope this helps.
pat