Beside autopay, refer your friend and family to PM. It is $1/ friend and it adds up. Just mention the reason you join PM and let your friend decide.
@Jessica1-33 here's a link on the rewards and their rules. https://www.publicmobile.ca/en/on/get-help/articles/reward-rules . I would also suggest using these articles to better understand the system since you are interested.
1 - The fastest and easiest would be the auto-pay.
2 - If you're focused on the fastest, it would be the community reward. It's actually the hardest to get (if you want to get 10$ or 15$ off), but it's the fastest, since you can grab coffee and spend hours on the community right about now!
3 - After that, the quickest would be referrals (1$/month/referral as long as they are active with Public Mobile).
4 - Finally, the real easiest (I know I lied on the first one...) but slowest is the loyalty, which is 1$/month per year active up to five years (5$/month off).