I'm not 100% sure how you want me to answer that question (as in what the answer should look like) but I'd say that I realised that, for Further Maths (forgetting about my other subjects for this case) there were 6 units to complete between September and... May, but I changed it to April to make sure there was enough time for revision. That worked out to roughly 1 month per module, which was quite a realistic target.
I then took the time at home to learn the content - the Edexcel textbooks were fairly good for this and I didn't need much external help, but there's always some available from TSR, examsolutions etc...) and went through each subsection of the book to practice questions until I felt confident with the topics. Because that's what maths is about - lots and lots of practice with an aim to 'understand' and be able to tackle unseen problems in the exam that may have twists here and there. And I guess around exam time I just looked at the spacing of exams and worked out what needed to be revised then, but in April I just did a few past papers for each module just to make sure nothing was missing.