Here is a link to ALISON, an Internet provider of free online courses.
If you are a first year student, this course might interest you:
You need to register (it is free) and you also have access to a wide variety of courses on different subjects, not only English Language Skills, but all of them are in English.
For other levels of English, you may access by clicking on English Language Skills from the main menu (see below). Attention to the display of the courses as it varies every time you access the main menu at http://alison.com/. This is what it looks like and if you click on the image below you will access the English Language Skills section directly: