For maths that u said ur weak in,theres only way to memorize the formula but not to solve the questions so constant practice is needed.For Chemistry,its important to know what is the outcome out combining the 2 substance most of the questions are base on that.for physics and bio,i have no idea because im not taking bio and i sux in physics..haha:)
bout the buku rujukan,i think pelangi is quite good.as for exercise,i think most of it are the same. all the best