Why do the ends of the leaves die?
Certified GKH Gardening Expert
This can be due to a great number of things. Has it been excessively wet? This can cause an infection which will do this. Wettable sulfur can help stop and prevent future infection.
Cold can do this as well. If it has been chilly in your area, then it will resolve itself when the weather warms up.
It could also be a deficiency if you don't fertilize at least once per year.
This article will give you more information on growing avocados: https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-tree-growing.htm