Here are a range of extensive video courses to improve your English skills:
BBC Learning English – YouTube: Hundreds of courses covering grammar, vocabulary, listening, punctuation, study tips and much more.
Learn English with Cambridge – YouTube: Hundreds more courses covering all aspects of English language learning.
Oxford Online English – YouTube: A range of courses in spoken English, Business English, study skills, pronunciation and more.
GoEnglish – YouTube: High quality, very clear videos on grammar and vocabulary.