There is NO MAGICAL FORMULA or SECRET METHODS as to why some succeed. This applies to everything we do, not just achieving good grades for Additional Math or Elementary Math. All of us actually know what it takes to be successful but we rather try to look for short-cuts or quick fix. Take a look at the video below from TED Education. It is a talk given by a psychologist/ex-teacher about her research on what it takes to be successful.

Differentiate $latex \displaystyle\ y=\frac{{{{x}^{2}}\sqrt{{x+1}}}}{{x-1}}$ with respect to x. Simplify the Numerator (otherwise you need to use both quotient rule for