For physics, most important is to understand the central concept
around each section of the topics you are learning. Drawing a
diagram to the practice problem, writing down the variables (eg. x
= 2 J , y = 2 m , z = ??? this is just my imaginary illustration)
and seeing which formula you should apply in the correct
context.
For chemistry, you can try going to Bras Basah complex 2nd or
3rd floor (first shop that you see on alighting from the escalator)
and buying the yellow book Step-by-step A level study guide
chemistry. I think there is a corresponding guide for physics
too.
Are you distracted by social media or your handphone? Try to cut
down on internet, have a study schedule and switch off your phone
if possible during studying.
All the best.