Avocados are quite slippery and can be a bit messy to chop.
Cut one avocado length wise and whilst still in it’s outer shell, get a knife and make signs both horizontally and vertically. Go deep as long the knife doesn’t come out from the other side. Then get a spoon or teaspoon and get your cubes out by scraping pieces away from their shell.
They will come out easily and without mess :)