How?

One approach is reading your and other people's written speech out loud. Pay attention to where it feels awkward; for me, that was the direction I needed to practice. A trick that I use currently to reinforce speaking written speech is using Grammarly to make corrections, which I try to internalize.

Another trick is don't correct words and letters. Say the sentence you really meant to say. It is not uncommon for me to say a thought or a concept two, three, four times in a row as I'm wrestling with what the language should be on the written page.