Create a story with your seed words. It's fairly ease to memorize even 24 words this way in a few hours. I did it when I took a stroll and always memorized 3 words at once. This way you essentially just have to keep 8 "things" in your head. You'll be amazed what your brain is capable of when you know how to use it (lol)

The real hard part is to be consistent and do this daily to be sure you will know your seed words when you need them.