The easiest way to crush an enormous ego is to fail a lot. Failing brings any great person down on their knees and welcomes them back to reality. But this can be detrimental to your sanity, well being and sense of security.
The second easiest way would be to volunteer. However, #2 doesn’t really work if you’re not in the right mindset. It feels like you’re out of place doing something you don’t want to do.
The third easiest way is to start thinking of what you’re grateful for, as opposed to what you feel you deserve. This changes how your mindset is and attracts things to come into your life, as opposed to having a sense of entitlement where you feel like you deserve everything.
Some people choose religion or spirituality too, but that would be up to your discretion. It shrinks your position in the world, but creates room for a God, all powerful being or a cause. Thus shrinking ego.
Or you can do what Barney from How I met Your Mother did. Have a daughter. That seemed to change his whole perspective in life as quickly as possible. She quickly became #1 in the world and he became #2.