I have been tutoring two JC1 students since sec 3 on an informal basis, and have helped them to exceed expectations in their O levels.
I believe in ensuring the understanding of underlying concepts over mere rote-learning and memorisation, as the former allows one to apply content knowledge to almost any question, while the latter only promotes inflexibility and ultimately does little to help.
During my JC days, I compiled over 300 pages of personal notes which I shared with my friends who I frequently helped, most of whom attained perfect or near-perfect scores in the A-Levels.