Why is it so crucial to use new techniques and approaches when you learn? Well... Learning a language is a long journey. You want to avoid the Einstellung effect as much as possible: when you routinely use familiar practices to achieve a certain result and miss out on much better ways to accomplish the same task. Be creative, be flexible, be smart about your learning!
Spaced repetition is a learning technique that uses increasing intervals of time between the review of previously learned material. For example: you review a set of flashcards not daily, but rather once in 2 days, then in 5 days, then in 2 weeks, then in 2 months, and lastly, in 2 years. Thanks to the psychological spacing effect, the information gets enhanced better when you review it like this. It works wonders for acquiring a large number of items. Imagine, what it can do to your vocabulary acquisition!
Gabriel Wyner wrote an entire book on how to use spaced repetition with language learning. "Fluent Forever" became an international bestseller. Recently, Gabriel followed up with a highly successful Kickstarter campaign, where he introduced a language-learning app largely based on the same principles.
Of course, you can create your own spaced repetition system in no time. Just mark your calendar and remember to come back to the previously learned material regularly.
You can also check out these apps. They are all based on space repetition systems:
the Mnemosyne Project
Recalling previously learned material by mentally retrieving key ideas is much more effective than re-reading or highlighting. Retrieval practice is a central topic in memory research right now. Free recall enhances previously done learning but also facilitates learning that is about to happen (subsequent learning). Isn't it amazing? It's called subsequent encoding effectiveness and it's going to rock your memory!
Do not copy the information from textbooks/teacher's whiteboard, but rather try to summarize it in your own way. Use a variety of tests to check how you retained the information. There are many language tests and quizzes available online for this purpose (check Transparent Languages). Study in pairs or groups where you can retell the key concepts to a partner and listen to her perspective on the same material. Teach somebody something you've been taught.
Alternating modes of thinking
In order to learn better, it's necessary to switch between two modes of thinking: a defused mode (allows you to relax) and focused mode (requires all your attention). By combining these two practices as a part of your learning routine, you will build and strengthen new neuro-structures that will boost your learning.
Combine intensive hour of grammar drills with one episode of your favorite TV-sitcom in a language you are studying. Sing a karaoke with Lyrics Training or Lyrics Gaps after finishing a laboriously crafted essay. Or just go outside and enjoy physical exercise between intellectual activities!
Alternate different senses, when you study: read a book and then play a Scrabble or try a dance lesson on YouTube in a language you are studying.
Hope it helps! Good luck!