What have you found difficult? What resources are you using? For me, I tried memorizing the rules for cases, but it was a complete waste of time: it was trivia disconnected from any usage of the language. What is (slowly) working for me is focusing on a single phrase with common words (e.g. в сибири, два пива).
Aside from the obvious resources (a good app/textbook; Anki), I have really learned a lot of the fiddly bits from this YouTube channel: https://www.youtube.com/user/russiangrammar