Write & Improve is the best way to improve your written English outside the classroom. Just choose a task and write about the topic. Submit your work and Write & Improve will award you a Common European Framework of Reference (CEFR) level, so you can see your progress.
A useful site for students & teachers. Lingro makes websites "clickable", so a user can click on a word s/he doesn't understand and the definition will pop up. There is no download required, making it safe and simple site to use.