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.
ナビ nabi This means Navigator (usually someone who gives directions in the passenger seat or the Navigation systems found in newer cards)
ニット nitto This means to Knit, knitting
カヌー kanu- This means Canoe
シチー shichi- This means City [Both syllables are not found in Japanese so SHI instead of SI and CHI instead of TI]
ナース na-su This means Nurse [Usually in Katakana English words the 'r' sound is implied by a ー but not spoken]