At this point you can add various ingredients to make it more "luxurious" but be careful not to overdue it. In my opinion, you don't want to add to many flavors to compete with the simple and clean flavors of the avocado, garlic and salt. I really believe that "less is more" in this and many of the meals I prepare.
The two most popular "additional" ingredients are diced tomato and chopped onion but some folks like to add fresh chopped chilies to give it a little heat.
You can try jalapeno, Serrano or green chilies but be careful not to overheat the guacamole.