1) Confusion of the 10 laws and how they co-relate with each other.
2) Confusion of negative indexes and how they can be solved.
3) Deriving the unknown bases and powers.
1) Check for errors in calculation whenever you are stuck or skip the question then come back to it to check.
2) Take your time when attempting a question so as to minimize errors during calculation.
3) Revise at home so that you are familiar with what you learnt.