Clean your mail list to avoid bounce. Don't use bought mail lists.

Set up authentication protocols (SPF, DKIM and DMARC).

Monitor blacklisting/greylisting.

Send relevant content to avoid being reported as spam.

Use List-Unsubscribe Header to make things simple for your subscribers.

Take care of URLs in emails (avoid broken links and shortened URLs).

Avoid using shared-IP to fully control your sender reputation.