It’s a someone idiosyncratic method, and while it worked for me in both Klingon and Lojban, I certainly wouldn’t recommend it for a natural language.
I did lots of translating from English. Lots and lots of translating. With some experimenting, trying to work out what looked more fluent.
(The question of what the hell fluency means in a made up language is a fascinating one. It does in fact have an answer. But that’s not what you are asking me here.)
This helped me memorize words and grammar which otherwise would have been a chore. And it helped me prioritise what I actually needed to remember for my purposes.
It occurs to me that one of the reasons this is a useful way of learning conlangs, is that there is a dearth of reading material. I did not need to do this for Esperanto, because there was plenty to read. Although I strongly suspect that’s exactly what the very first generation of Esperantists did.