Remember that the quality of your revision is always better than quantity. Try not to overwork yourself as you'll burn out and it may affect your results in the end. Always go over a topic after learning in class make revision materials ad test yourself with flashcards and make sure you consolidate the knowledge. If you struggle with a particular topic or concept don't hesitate to ask your teachers, there's no shame in wanting help it's their job! Take every day as it comes and try to improve little by little and you'll get there! DO NOT COMPARE YOURSELF TO OTHERS because that will definitely affect you and may make you feel unmotivated. But I'm sure you won't fail. Be kind but firm with yourself. Set new and REALISTIC goals every day. Just try your hardest tbh and put the work in NOW so it's easier for you later. And in the end don't be disappointed about the grades you didn't get, be disappointed about the work you could've put in. So just stay focused on YOUR OWN grades and study. I know you'll do well!
From personal experience, I've always found practicing past papers to be the most efficient for me. Past papers allowed me to familiarise myself with the types of questions I can expect, which topic areas I need to improve, and helped me to apply the pre-existing knowledge I gained from revision into context. Another tip I adopted while doing past papers (typically for the sciences) was to sought out for those large 5-9 mark questions and write it on a flashcard. On one side I would have the question, and on the other side I would have the mark scheme. Often times I would try to paraphrase it without straying too far from the answer to help me remember it in my own way and strengthen my understanding. This technique was extremely useful for my biology papers.
I agree with @myopeia, another useful tip I found useful during my GCSEs was to go over the notes I made in class when I reached home. I would exclusively re-read the notes, add to them, and try apply it to questions for the topic I learnt that day in class. I've found that doing this helped me retain the information longer, and strengthened my understanding of it. By doing so, it also allows you to revise your syllabus in smaller, digestible amounts.
You can also try out new revision techniques and try find one that best suits you, we have an article that thoroughly explains techniques all students can find useful: https://bit.ly/3uCzvZl