Perfect avocados are key for a good guacamole. To test avocados, gently squeeze. An avocado that's rock-solid isn't ready. If it's a little soft, it's probably ready. If it feels hollow, it's too ripe. Place unripe avocados into a paper bag with a ripe banana overnight to speed up the process. Put perfectly ripe avocados into the refrigerator to prolong the perfection. Throw away overripe avocados, and try again using the these tips. PS - the same logic applies to mango!