I've been trying to become fluent for over 12 months, having been passively exposed to this language for over 9 years. I'd say that mastering English beyond intermediate level is extremely difficult.
You have to be constantly aware of what you are saying. Also, you need this kind of loopback that allows you to detect your mistakes and learn from them. This is a difficult skill which requires practicing.
You also need to have a social and communicative personality, so if you are introvert than you are less likely to master a language. I am focusing on speaking, because it is the most important aspect of any language.
As others said, when encoutering a new word you should check the pronunciation and commit it to your memory. This in turn allows you to practice your inner voice while reading. If you don't do that, then after some time you will reinforce your accent.
I know that this is irrelevant, but is it worth the trouble to learn an esoteric language such as Rust? For me it seems a waste of time to learn a language along with its ecosystem where there are few job prospects.
Right now Go seems to be on an upward trajectory, and despite its ugliness and how primitive it is, it is the job which can pays off when hunting for jobs.