What a GREAT question! Thanks for asking.

The easiest preparation is to try to “purify” yourself, typically via Confession. That’s why most parishes have Saturday confession so you can go to confession before going to Sunday Mass (and if a fallen Catholic makes it known that they’re returning after a long time away, priests will encourage them to go to confession before receiving the Eucharist).

When I was a kid (and long before), Catholics were encouraged not to eat between the time they went to bed and after the time they went to Mass (so we get the word “breakfast” from “breaking the fast”). Today, most priests say an hour fast is good enough.

The absolute best way to prepare, though, is prayer. That’s why people are encouraged to get to Mass early, to have some time to pray before the Mass begins.