The main work is in pruning your list regularly to remove known bad email addresses, or addresses that are bouncing. If someone unsubscribes, make sure they’re removed immediately. Asking people to add your email address to their contact lists can help their servers recognize your email as legitimate, making it far more likely that it will be allowed through.
Eliminate duplicate email addresses. If your email marketing service provider (ESP) does not do this automatically, do it yourself manually. Remove fake accounts, or addresses that were entered as a prank or are plain nonsense. Look for addresses like abcd@, qwerty@, test@, and any other common bogus user names. These are all entries that you absolutely want to get rid of as they are wasting your time/ money and dragging down your email sender reputation.
Frequently monitor your list for “no opens” and “no clicks’ to determine who is no longer engaged and remove them from your primary mailing list. If you are reluctant to let go of these contacts, consider moving them to a separate list for re-engagement campaigns.