I use the journal from this site, but you can also make your own. Simply put, Tesla believed the numbers 3, 6, and 9 had a lot of power. I write my manifestations 3 times in the morning, 6 times in the afternoon, and 9 times in the evening.
I think it’s a great activity, even for people who don’t believe in manifesting, because it helps you narrow down your goals and figure out how to achieve them. Sometimes I have so many ideas floating around that it’s hard to focus on what I truly want. The 369 method helps me.