Study Skills (Study Guides and Strategies) - http://www.studygs.net/
Study Skills (Virginia Tech) - https://ucc.vt.edu/academic_support/study_skills_information.html
Study Skills (Academic Tips) - http://www.academictips.org/
Study Skills (How to Study) - http://www.how-to-study.com/
Academic Help by subject (Khan Academy) - https://www.khanacademy.org/