Reading - Try to read as much as you can, books, articles, etc and keep on a sheet all the words that you don't know.
Listening - I think that the best way to improve in this field is watch (and then listen) news channels on tv as bbc news, cnn, etc. They also provides a lot of subjects to hear about.
Speaking - No advices, sorry.
Writing - As reading, if you read a lot, you will able to use new structures and new terms. Try also to use the adequate transitional words when you try to explain your point of view.