Traditionally, pull processing would refer to under-developing over-exposed film.
However all my tests on varying the development times for Portra films (i.e. pushing and pulling), were done with film that had been over-exposed by 1 stop.
You will find many photographers who routinely over-expose colour neg by 1 stop - it's simply a safeguard against underexposure.
Underexposed colour neg looks bad, whereas over-exposed colour neg - by 1, 2, even 3 stops - looks almost identical to normal exposure.
Start with a good exposure (1 stop over), and then create different looks with push and pull processing and different papers and techniques (e.g. pre-flashing) in the darkroom.
(Alternatively expose normal, process normal, scan and do what you like in photoshop.)