The most difficult thing for me is learning new words and verbs along with pronounciation (stress).  

None of them sound or look anything like English.  I have to learn new sounds along with shapes for words to remember them.  

Cases are tedious, but not insurmountable.  They just take time to learn and memorize, but words don't follow patterns like cases.  At least, not that I have seen.

Prepositions also follow patterns.  Those which do not, just need to be memorized, there are only so many of them and only so many situations when they are used.

падежы,исклонение

Which difficulties?

I make LOTS of stupid mistakes. Just mistakes in things I've been knowing for a long time.

And prepositions. :D

А lot of unfamiliar words.

the grammer is difficult, and the pronunciation