You don't need to study every day and night, just do what you think is required, and self-assess yourself regularly, eg, once every month or so. Set yourself a mock paper for what you've done so far in the year, cram revise for a day, and see how effective your study routine is. Increase or relax the intensity of studying you do accordingly.
If you're doing sciences, then this applies:
You do not need to learn Biology/Chemistry/Physics, or even have more than a superficial understanding of the topics you're covering. What's far more important is knowing how the exams are structured, reading through past papers and mark schemes many times over, learning the phrases that always get marks, learning the perfect responses to stock questions, and acceptable alternative words.
Learn to the mark scheme. This will get you high marks. Sure there is some thinking required for many questions in the exam, but pretty much all exam questions fall into one of these categories for science:
Regurgitate fact or definition; <-- Look at mark schemes for the approved version and the 'vital' words in it.
Apply rule to situation; <-- You learn laws and rules for science. If you know these by heart and have basic logical cognition, you can do these questions. May require factual knowledge too. Very basic maths ability required sometimes.
'Stretch' questions; <-- You apply a rule or law to a situation which is similar to what the rule is normally used for, but is disguised. These are normally easier than they seem and just require you to replace words in your factual knowledge or laws with the situation given in the question. The mark schemes show alternative approaches and let you get used to these.
Science A-Levels are a memory game. Learn off the past papers and mark scheme and specification. Don't get fooled into thinking you need genuine understanding.