If humans were ever able to travel to a distant planet (light-years away), what preparations would have to be made?

First of all you’d have to prepare for the trip which would take hundreds or thousands of years. So you’d need to have a generational ship. Whole generations of people, including you, will die on that ship and their offspring will grow up and die, and their offspring and so on.
Many generations later they will arrive and hope that somebody figured out a way to slow the spaceship down, because it would have to be going pretty fast to get to our nearest stars in that amount of time.