Using citrus zest without making a dish bitter

I've started using citrus zest to brighten pasta and vegetables, but my first attempt made the dish bitter. I probably grated too deeply into the white pith, then cooked the zest aggressively in hot oil. I'm going to use only the colored surface and add some near the end. Do you prefer a fine microplane or thin strips for controlling zest, and when does cooking it improve versus damage the aroma?