I assume you just need more practice. You could try doing a 30-day writing challenge: https://writingcooperative.com/should-you-do-a-30-day-challenge-to-improve-your-writing-f48dd37f50c3 That can also help writers find their unique voice.

Also, make sure to use a grammar tool like Grammarly (works only on Chrome for Medium) or LanguageTool (also works on Safari and Firefox etc. for Medium).