How do I know which method of diffirentiation to use?

The main methods of differentiation you need to know at A level are the chain rule, the product rule and the quotient rule.

The chain rule should be used when the eqation is a function of a function. E.g. y=x^​(sinx)

The product rule should be used when the eqation is a product of 2 things E.g. y=x⁴ln(x)

The quotient rule should be used when the equation is a fraction. E.g. y=(2x+1)(4x²​-1)