I do Edexcel, but I might as well say how I did A level Maths. It might not work for you but it worked at least for me.
I taught myself the AS content as fast as I could by myself. And when I mean fast, I mean really fast. I'd make notes on what ever exercise in the book came up. If the exercise had a really simple concept and I didn't think the questions looked too difficult I'd only do a few of the questions. Just to give some sort of example, there is a chapter called "2nd Order Differential Equations" in the Further Pure 2 Unit of A2 Edexcel Further Maths. I read what the textbook had to say, and tried to teach myself the concepts behind the method they used. And all it really boiled down to was solving a quadratic equation. There were 30 questions total in the first 3 exercises of the chapeter: I did 3. If I was struggling a bit, I would do most, if not every question of the exercise. If a concept was more difficult to understand I would use Khan Academy, Exam Solutions (unfortunately for you though, Exam Solutions is mainly Edexcel focused), or anything I could find online to help me. The vast majority of the time it worked, but if everything else failed, I'd go ask a teacher. I used a different text book to what my school used so that by the time the classwork caught up to where I actually was, I wouldn't just be doing all the questions twice. School work then just becomes extra revision
The reason why I say to cover the content fast is because if you do, you don't have time to forget anything. And then you start past papers, which revise everything at once. This is how you get your grade to shoot up. When I started the past papers I didn't do very well; I never expected to. but you start to get the hang of it. I did a past paper for each unit maybe every other day, the marks I got went up and the time it took for each paper went down the more I did. In 2 - 3 weeks I was getting the marks I wanted. And then what happens after you've finished all the past papers? Well, you do them again. Chances are you will not remember absolutely any of the questions from the first papers you did; I know I didn't.
And once you've done that, I would say don't be afraid to venture into other maths boards' past papers.. Some of the content may be different, but maths is maths. Everyone pretty much learns the same things.
The main reason why I like Edexcel is it because it has the largest online set of resources out of all boards from what I've seen. We have extra "supposed to be more difficult" Solomon past papers papers and everything. (They're just some extra papers some random guy made). The Edexcel textbook really helped as well, because the textbook came with a solution bank to all the questions so if I ever got stuck in the teaching myself process It was a lot easier for me to figure stuff out. Unfortunately I'm not sure if OCR textbooks are like that.
If you are confident in your Maths ability and can put in the extra effort, then I would recommend this method. If you've never taught yourself much before you might find it really difficult, because I did when I started doing this. But when you get the hang of it, you can pretty much do it for some other subjects, especially the sciences (though I revise science a little differently). Humanities subjects, well I've got no advice for them. I hate essay writing.
Remember, this is just how I revise Maths. It might work for some, it might not for others. If you think it might be worth a shot, then I don't think it'll hurt to give it a go.
Also. Physics and Maths tutor is a brilliant website for resources of all boards. Unfortunately the website is kinda down at the moment. All the links have been removed due to a server move.
Oh yeah and calculator :
https://www.amazon.co.uk/Casio-FX-991ESPLUS-SA-UH-FX-991ESPLUS-Scientific-Calculator/dp/B0034BAQS8/ref=sr_1_1?s=officeproduct&ie=UTF8&qid=1471019469&sr=1-1&keywords=casio+fx-991es+plusI have this one.