Let's take a look at the N's. You may want to make flashcards to practice by. "Na Ni Nu Ne No" is fun. Sounds a bit like something Mork would say to Mindy... Also there are no unexpected sound forms here.
Write them out 10 times a day and soon you will get it. To aid memorization, make silly associations to go with them. You can use the above mnemonics or you can make your own!
ナビ ____________ This
ニット ____________ This means ____________
カヌー _____________ This means ____________
シチー _____________ This means ______________
ナース _____________ This means ______________
ソナー_____________ This means ______________
Perhaps you can recognize these 5 in just one day of practice.