The easiest way to get started with OKRs is to start using them.
There are a lot of resources you can read and watch before, but to understand how they work, they need to be tested on your team.
It is very common to finish your first quarter with mostly 100% or with mostly zeros, especially if you had no prior experience in setting OKRs. It’s important to remember that OKRs are not a project you run for 3 months. To work well, they must be used constantly and the progress must be improved every quarter. In 3 or 4 quarters, you should have a clear idea on how they work and most of your KRs should fall into the 70% category. Then you’re all set.