My trick which often works is that the word for 'my' for 'et' nouns ends in 't' as does the word 'et' and for 'en' nouns 'my' ends in 'n' as does the word 'en'. Plurals are great - the word for my ends in an 'e' as most plural nouns do. Et nouns = mitt En nouns = min plurals = mine.
Same rule with 'your' & 'their'.
Hope this helps someone who might think like I do - scary!