A trick my German professor gave us to remember cases and prepositions
(TEACHERS HATE HIM because of this ONE WEIRD TRICK!) I couldn't resist.
He explained that certain prepositions almost always take certain cases. We've only covered accusative and dative (which luckily seems to be the order here on Duo!) and I find it super helpful.
For Acc. there are 7 commonly used ones:
Gegen Durch Fuer Ohne Um
For Dat. there are 9:
Aus Ausser Bei Mit Nach Seit Von Zu
He gave us a couple of melodies that match. For Acc. you can sing the tune of "London bridge is falling down," as "Ge-gen durch fuer, oh-ne um, oh-ne um, oh-ne um." Und so weiter.
For Dat. you can use the melody of Strauss' Blue Danube Waltz. "Aus ausser bei mit, nach seit, von zu." (Because I realize that there might not be many music nerds out there, here is a link: https://youtu.be/_CTYymbbEL4 Everyone has heard it before, and the part you're thinking of is probably at 1:33)
Hope this helps!
Good suggestion to use melodies for learning! You might want to edit the spelling in your post, though. Außer is spelled ausser if the ß is not available on your keyboard (always replace "ß" with "ss".) This is important as it affects the pronunciation: ß and ss indicate a sharp s and a single "s" is pronounced like our "z". Also, it's not "seid" but "seit".