The answers below contain advice and links to resources on how you can help humanity navigate existential risk from AI. They branch out into specifics depending on your preferences, background, and situation.
Our general advice is:
Start reading about parts of the issue that you find interesting. For example, you could look up concepts on this site, and follow links to resources from other answers.
More specific advice will depend, first of all, on whether you’re looking to make AI safety a major focus, or whether you’re looking for ways to help that don’t require that level of commitment. And before deciding to take big steps to contribute to AI alignment, consider whether you’ve “put your own oxygen mask on first”: are you in a good enough state in terms of finances, psychology, and health?