There are a lot of practices and most of them require handling with care your Email List and your Template. And the most important is the IP reputation which it affects where the email lands. I recommend the warm-up procedure from time to time since it can really be the most important when your emails don't land where they should. At ZeroBounce there is also the Inbox Tester which can be a nice test for your Template to see where it lands. As a conclusion, don't overlook the IP reputation and warm-up the IP from time to time and also be very cautious with the words in the Email Template. Hope this helps!
Never Use a Web Client to Send Marketing Emails:
If you are using an email client like Outlook, Yahoo, Gmail, Thunderbird, or AOL to send email marketing messages, stop now. Using your own email is one of the worst things you can do. Instead, always use a company email address.
There are plenty of options for email marketing providers that can help you create and send professional spam-free emails that will impress your recipients. Some, like MailChimp, even offer free limited accounts (up to 2,000 contacts), while others offer reasonable rates for larger lists. So take a look around and see which one works best for you.
Always Use a Permission-Based Email List:
Recipients who are well aware that they have permitted you to send them emails will be much more likely to interact with your marketing messages and much less likely to report you as spam. This is important because of increased engagement and better ROI and because too many complaints will increase your SPAM score and prevent you from sending emails to anyone.
Use Email List Cleaning:
Now, you already know that how a spam score works. When you send emails to an invalid email address, you get a Hard-Bounce. Ultimately it will hurt your domain reputation. So use Email Verification or Email Checker tools for the email list and then send the emails; by this, you can be fully deliverable.