The best way to tell whether your fruit is ready for harvest is to pick one nice, large, dark avocado from your tree, and then leave it out on the counter at room temperature.
At this point, the thing is rock hard. You can practically use it as a pestle for your mortar, or even a weapon for self-defense. Have you ever dropped an unripe avocado on your toes? Oy, it’s not pleasant.
If the fruit softens evenly within a week or so, then the rest of your avocados are good for the pickin’. If the fruit turns rubbery, shrivels up, or tastes bitter, then it isn’t quite ready yet.
Keep checking every other week by picking one fruit at a time until you find an avocado that ripens to the right consistency and flavor of your liking.
Once your avocados come into season, continue picking them regularly so they don’t over-mature on the tree.