Useful online resources
Other useful websites
Improve your reading
Try to read something in English everyday. You don't need to spend a long time, but doing it often will help you improve.
Improve your listening
Try listening to something in English everyday. You could watch Youtube or Vimeo, or try these listening activities.
Graded readers are also useful.
Improve your grammar and learn new vocabulary with these apps...
The BBC and British council have excellent websites where you can find a lot of interesting material.