When revising you want to be as effective as possible to ensure you are absorbing maximum information in minimum time.
Studies have shown that writing notes, rereading and highlighting work is the most ineffective way of revising and will not get you top grades. However active recall is the top best method for studying and retaining information for the long term. The act continuous testing of one-self is the easiest and simplest way to learn information. So using Quizlet is a good site as it's based on active recall. Doing past papers is arguably the most effective revision technique and is where students saw the most improvement in grades.
Another study also showed how students scored better when they repeated a topic over time so they would revise the topic on day 1 and 2 then take a break and come back to the topic on day 4, the study showed that it was the most effective method for retaining the information and thus scored highly on the test.
When revising try and rely more on understanding rather than memory, it's a lot easier as you have less things to learn but you can still get the correct answers as you understand the basic mechanism of how the things works and can use logic to reach to the answer. E.g in chemistry you need to know trends of reactivity for group 2 but if you know that electrons are the factor that effects reactivity using logic as you go down group 2 outer electrons are further away this means they can leave more easily and that's what we want in the reaction so going down group 2 reactivity increases. The use of logic and understanding means you have to learn less information but still have the same amount of knowledge.