From my personal experience, I found out that reading, understanding and speaking are skills that are the easiest to develop when you learn a language by yourself and when you get the chance to live in countries where Russian is spoken. What I find hard is to develop writing skills, particularly writing eloquent and argumentated pieces of texts such as essays or text commentaries. Because of course, when you learn independently, there is hardly anyone to correct your сочинение...Would anybody have some tips on how to develop written Russian expression skills?