Mark the location of the planned soffit vent. Use the template supplied with the vent or the measurements of the portion of the vent that includes the opening. Position the planned vent location where it doesn't interfere with light fixtures. Place the planned opening between two rafters.
Drill 1/4-inch holes at each corner of the planned vent hole.
Cut between the holes with a jig or circular saw. The jig saw is preferred because it is lighter and easier to handle when working overhead and on a ladder. Clear any insulation that may be in the soffit to prevent clogging of the vents.
Install the vent, placing wood screws through the vent cover into the soffit material around the vent hole.