You will find all sorts of suggestions online for the best way to store guacamole and prevent it from turning brown, but the reality is that none of them work well. Guacamole needs to be made fresh or just a few hours ahead of time. If you're not planning to serve it immediately, press a piece of plastic wrap directly over the dip and refrigerate for up to two hours; after that, it will start to deteriorate. Be sure to bring it to room temperature before serving.