Believe it or not, avocado pits actually help keep the guacamole from browning. Just add the pit on top of the dip and then cover the bowl tightly with saran wrap. Make sure the plastic wrap is directly on top of the guacamole so that there isn't any air coming in contact with it. This should help slow down the oxidation process, which in turn will keep it from browning too quickly. Even if there is a brown layer that forms, you can just scrape it off and find a nice green layer right underneath.