Store guacamole in an airtight container, and seal the guacamole from exposure to oxygen with water, lime juice, or avocado oil. I usually use glass containers with snap-lock lids for storage and follow this procedure to prevent browning: - remove air pockets by pushing on the guacamole all across the surface and sides - smooth the surface of the guacamole so it is flat with no peaks - cover the surface of the guacamole completely with water, lime juice, or avocado oil (I use avocado oil) To use the guacamole, pour off the liquid or oil (I reserve this in case I will not use all of the guacamole and need to refrigerate leftovers), use as desired, then repeat the procedure from above with the reserved liquid or oil for any leftovers. Vacuum sealing also helps retain freshness (these FoodSaver canning jar sealer attachments are great for vacuuming the air out of canning jars; affiliate link).