With .38 super I think you could use the slide weight, but if you do decide to port the way I did, remove the front sight first. Clearly mark where you want to file and which lines you dont want to file past.
Good luck. Just dont rush it. Also, you way want to start with a triangular file to create notches that will help keep the round file aligned. Space your ports evenly and stay away from where the locking lugs are in the slide.
In order to make it easier on yourself, file two ports on one side and two on the other. Then if you feel like it add a port on each and so on. This way you won’t lock yourself into a certain number of filing one side completely and then having to repeat that same number on the other side.
I generally tried to follow the angle of the grip for the ports, but it may be easier to file perpendicular to slide axis.
Oh and don’t get too close to the front of the slide where the barrel bushing locking lug slot is.