There are 2 levels to this answer:

1. Your technical sending infrastructure. This is a must have to get your emails even just delivered to the mailbox. This includes IP reputation/Senderscore, domain reputation, being on any whitellists or blacklists etc. You need to have this in order not to get blocked.

2. Your engagement metrics. OK your emails are getting delivered but are they making it to the inbox instead of the spam folder? This is about choosing the subject lines, email content, email format, send times and days that generates the most engagement (open rates, mostly). This will help your emails avoid the spam folder which in turn will reduce your likelihood of your emails being blocked in the first place