For me it depends on the subject and what works best for you. I would play around with some different study methods to find out what works well for you, as not everything will work for you. The one thing I will say is to try active study methods over passive, as these methods will be best to retain the content.
For me:
I find quizlet great for only one of my subjects, which is based more on memorization. It is time efficient as you can type them, and the test feature is awesome. Plus less paper to store! So I would only really use this for memorization/rote learning definitions, certain scenarios etc.
However, when it comes to other subjects I find it isn't effective enough, especially for more application subjects. For science and maths subjects, practice questions will be your best friend over something like flash cards unless you need to memorise a definition.
For english subjects it is also just doing practice essays and getting feedback from you teachers. It is really the best way to improve, but also to make sure you go in depth with your texts so you understand the themes, characters, their motivations, structure of the text, key story lines etc. You can do summeries either hand writing or typed, maybe make a poster on a chapter or character.
So as you can see it can really depend on what subject and what you like. If you think the flashcards are working well for you, keep using them. But some other methods could be:
-Writing topic posters. E.g, grab an A4 piece of paper, write down a heading of a topic, dot point in a study design etc, and write everything down via sumerising everything in that topic.
-Make you own questions or tests.
- Answer practice questions from a variety of resources, but mainly textbook and VCAA.
-Teach it to someone. I really like to talk about english and food studies to other people, it allows me to consolidate the content and get me to explain it in laymen terms.
There are a few other, but these are some really active learning methods which will really help with your study. Good Luck!