I got grade 8 in physics, in year 10 I probably got around 6-7.
And for physics, learn the equations. It sounds tedious but it means that when you are in the exam all you need to do is rearrange and substitute the numbers into the formula.
Make sure you convert numbers in questions to the correct units by looking at their prefixes (e.g. MegaAmps).
Practice questions and get familiar with topics that are bound to come up, for example circuits, learn what DC and AC is, learn what current, voltage and resistance are (I'm not kidding learning what those actually are got me so many extra marks). Once you understand WHAT things actually are in physics it becomes much easier. Hope this helps!