As mentioned in the PR, I reviewed some code before and then found something which I thought could be improved.

Before contributing, I was intimidated since my C++ skills aren't really that great. But I thought this can change over time.

So when I decided I really want to contribute to bitcoin, I first read some articles like this one from @jonatack. I also lurked on Bitcoin PRs to see the process in action and joined the Bitcoin PR review club twice. (It's every Wednesday at 17:00 UTC on IRC but I always forget about it lol)

I also cloned the repository and checked out the code to get familiar with it. I haven't run the test suite yet, though.

But as @jonatack and others mentioned: Just start by looking over existing PRs and try to understand what they are trying to change! Reviewers are definitely needed the most.