Having experience in other languages it should be fairly easy to pick up. I personally bought the book Let's Go by Alex Edwards. It's a project based book where he teaches you Go by writing an API server. I found it really beneficial as I was familiar with API development but not with Go. After that I used what I learnt to create some side projects and the rest is history.

If you feel you're already past that point of learning then I'd just create little projects. Re-write one of your old ones in Go, and things like that.