Below are the important points that you can keep in your mind for solving numericals.
1. Read the question thoroughly.
2. Note down the quantities that are given in the question.
3. Remember the formulae in the text and apply them in the numericals.
Below are the important points that you can keep in your mind for deriving an expression.
1. The beginning of the derivation is important.
2. Involve all the necessary steps in order to lead you to the correct expression.
3. Involve all the needed explanations for the steps involved in the expression.