Acting upon the information you've gathered can be a challenge since the answer is never a specific step by step list of what exact changes you need to make.
The good news is that the internet has made information-sharing much easier and nowadays there are many sources you can gather information about fixing delivery problems.
Remember: deliveries fail because recipients do not want the messages. So fixing delivery problems means finding what kind of mail the recipients want to receive. That's the only real way to fix the long-term problem or ask bulk email store