Some good youtube videos for economics include Acdc economics (something along those lines), pajholden and khanacademy of you are more of an audiovisual learner. Also, getrevising has a few revision notes of high quality that I am rewriting in my own words.
As Turbo said, using notes and documents to answer exam questions and then trying without notes is an effective way to not only revise the content, but nail the exam techniques too.
Instead of flashcards, I use this app called Evernote, which is a great note taking app which I type my notes up on my laptop and it syncs with my phone, giving me access to these notes at all times, even without internet access.
Obviously, revision guides are a good way to revise, but instead of reading a topic front to back, read it back to front. This way, you first get a summary of the content, then the detail which is useful.
Economics help and tutor2u are good websites to refer to when revising and I also use them for diagrams
Having a copy of the syllabus is great as it allows you to track your progress and see what you need to know for the exam.
Good luck with your revision and exams