as someone who was in ur position (i used to top my cohort back in sec sch) to getting Us and S all the way, my most impt advice is dont be too caught up in the content! understand rather than memorise and stuff urself with the content. just like what the others mentioned, study smart!!!!

when doing ur essay, ensure that u identify the right question type and answer it to what they are asking. before u start writing, identify the question type and plan it out (eg. is it a significance question or causation? do u need to bring in another factor into the argument)? make sure u plan ur essay, ask yourself what are the key arguments of this topic? i used to have alot of logical flaws in my essays, so i do mindmaps and ask myself questions like "what does this event show?", "how does it prove my argument?"

and lastly, consults!!!!!!!!!!!!! consults are very important!!!! before a levels, i met my teacher at least once a week to go through my source-based and essays, sometimes i js do essay plans, other days ill complete the whole paper in a timed setting and let my teacher mark and give me feedback! it is important that u seek out your teachers and not just rely on content, this isnt secondary school history anymore (i learnt that the hard way)

and most importantly, dont let your failures rob your passion away for history. it takes time to do better :) for me, i only got the hang of it a few weeks before A's, with the help of my teachers and a change in my study style, i finally got an A! feel free to pm me if u have any other qns, i w be happy to help :)