https://www.google.com/aclk?sa=l&ai=DChcSEwiwg-2sk-mFAxWnUEcBHZrrDwcYABADGgJxdQ&sig=AOD64_0oQXfCtc5imGr2Qjb-qgFzkuOovQ&ctype=5&q=&ved=0ahUKEwjvy-Wsk-mFAxWPFFkFHZFSAKMQww8I9hQ&adurl= is one of the best books on the subject. For me, i’d say it came down to a combination of gradually building my retention over time through regular dream journaling and meditation. I also suspect psychedelics may have played a bit of a role. Hope that helps!