Fresh cilantro and lime juice are to guacamole what milk is to a chocolate chip cookie. Resist the temptation to used bottled lime juice. A whole lime or two squeezed into your guacamole, along with a handful of chopped cilantro, will provide a welcome burst of brightness and astringency to your dip. A bonus: Fresh lime juice slows down the oxidation process (preventing your guacamole from turning brown).