Dice tomatoes, onions, and jalapenos into small cubes (onion and jalapeno should be diced finely so it's not too chunky)
Cut your limes for squeezing later, and chop up the cilantro
Grate your garlic clove (I like using my microplane grater/zester to make it very fine)
Chop avocados into cubes. I like to slice the avocado while it's in the shell, and scoop it out with a spoon.
Add half the avocados, the grated garlic, salt, and lime juice to a bowl. Mash together until it's smooth.
Add in the rest of the ingredients and lightly mix together until everything is incorporated.
Cover the top of the bowl with a cling film, pressing it onto the guac so there's no air in the middle (this will keep it from browning). Let it rest in the fridge for an hour for best flavor. Enjoy!