Akbar, this is an interesting topic to be discussed here. I do hope that other members, especially foreign language learners can actively participate in this forum category, particularly in this thread. Therefore, I encourage anyone who read this, you are suggested to read and answer these questions. Your answers will be valuable not only for the researcher, but also all of us here. It is possible for you to get an inspiration by seeing someone's way to overcome his or her problems in writing.
With regards to my own obstacles in writing, I reckon that it is definitely grammatical accuracy. This is the most terrifying issue for a foreign language learner like me. In 2 or 3 years ago, I was afraid to write anything in English. I felt that my ability is a shame compared to others, especially my classmates in university. Therefore, I did some practices by reading some English articles and grammar book. The book that I used at that time was Betty Azar's book, Understanding English Grammar
(the blue one). By consistently doing those efforts, I was able to earn a satisfying mark in writing within a semester.