You always want to start with a ripe avocado. If you press your finger into it, you can tell the avocado is ripe if it has a slight give. Ripe avocados are generally a little darker than their unripe siblings, but this measurement is a little less accurate as some varieties of avocados stay green even after they’re ripe. If your avocados aren’t turning fast enough, you can speed up the process by placing a couple of them in a tightly-closed paper bag. Still not quick enough for you? Throw an apple in there to really kickstart the process.
If you’re worried about your avocado turning brown after it’s been cut, a good way to preserve the beautiful green color is to squeeze a little fresh lemon or lime juice over top and cover in plastic wrap.