To perform well for A level Physics, one of the prerequisites is that you need to be well-versed with your O level mathematical skills especially trigonometry and ratio method. If you have forgotten these concepts, I would strongly advise you to re-look at it again before school starts.
For example, based on one look at the following diagram, you must straight away tell that the component of weight of the block which is parallel to the slope is given by Wsin30°
Another common trigonometric skill you need is to be able to solve for the possible value(s) of θ given an equation such as 15=25sinθ. [Ans: θ=36.9° or 143.1°]
You should also read up on your O level Physics concepts because most of them will be covered again but at greater depth. Just to highlight a few, you need to be very well-versed with the Kinematics equations, drawing free body diagrams, forming resultant force equation, applying principle of conservation of energy, relationship between potential difference, current and resistance, using right hand grip rule and Fleming’s left hand rule etc.
More importantly, A Level Physics is a very hands-on subject, merely understanding the concepts in the lecture notes will not be sufficient to help you get your As. Instead, you should be spending more of your time working through practice questions to hone your problem solving skills and application skills.