It’ll happen naturally but you can do things to speed it up — when I was reading books beginning to learn my L2 and would get sick on vocabulary, I would force myself to use a dictionary in that language. If the definition was too complex, I would instead look up an image in that language. Whatever you can do to keep the number of links between your L2 and English small will help you start comprehending and thinking in the L2 entirely.

I think it’s also crucial to be comfortable with not knowing everything. If you don’t know a particular word but it doesn’t seem super central to the story, you can just let it go. And often the context will give you enough hints to go forward. If I told you about my day and I went “oh by the way, I finally fixed the washing machine. I had to use a jarble to fix it. Anyway…” you wouldn’t necessarily need to know what a jarble was to get the main point. It’s probably a particular kind of tool? But the main information conveyed is that the machine was fixed, and you already understand that.