Make a habit of practicing your native tongue
This sounds obvious, but it’s something I wish I did when I decided I wanted to be a translator: Practice writing in your native language.
A lot.
Interpreters are different, they also have to use their second language a lot, but translators, you’re paid to do well in your first language.
Even if you don’t publish, it’s very helpful to keep up your writing practice if you’re to do well.