YouTube Premium offers a free trial (usually 1 month) to new subscribers. Each new Google account qualifies for its own free trial.
// Step-by-step walkthrough
01
Create a brand new Google account (this requires a unique email, which Google lets you create for free)
02
Log into YouTube with the new Google account
03
Navigate to YouTube Premium and look for the free trial offer
04
Start the trial with a payment method on file (set a reminder to cancel)
05
Enjoy ad-free YouTube, background play, and YouTube Music for the trial duration
06
Cancel before billing starts, then create another new Google account for a fresh trial