I have trouble with some of the consonant sounds Icelandic lacks. し/じ/ち/つ/づ/ず and any other sounds with the same consonants. I can’t really pronounce them and have a hard time hearing the difference between them. It makes some of the rendaku hard to remember too
I have had success transforming some of the particles into cases in my head, の is like the genitive, に is somewhat like the dative, を is somewhat like the accusative. It is never 1:1 but rewiring word+particle as word+case made the grammar much easier to think about