For maths questions I feel that getting your head around the concepts are difficult but once achieved allow you to comfortably answer a wide range of questions. Therefore for maths tuition I think it is important to find a method that works for the student and then practice using it through multiple questions.
Obviously it is easier to discuss concepts face-to-face however for this example I've found a four step process helps me answer questions on the chain rule.
1) Differentiate the thing in the brackets
y = 2x+1 --> dy/dx = 2
2) Multiply that by the induction outside the bracket
2 X 3 = 6
3) Stick this number before the initial bracket
6(2x+1)^3
4) Minus 1 off the initial indicy
6(2x+1)^2
So dy/dx = 6(2x+1)^2
This is just one method. There is another one substituting U into the equation and then saying [du/dx X dy/du = dy/dx]. I would go through both methods with the students so they can use the one that works for them.