First, you must understand it. Do not ever try to memorize, because memorizing does not work in mathematics at all. Try to understand the basic of the theory. Once you have understand it, you can slowly solve all the questions given.
In order to improve yourselves in Add Maths, you need to do more practices. Maths questions can be asked in many ways. By doing more practices, you can get yourselves familiar with the basic of the theory or even have a better and deeper understanding about it. Of course, you are also able to get a brief image of ways of questions being asked and methods of answering the particular questions. Do more practices, until you are okay with it. If you don't know how to do it, refer to the answers. But of course, do not always rely on the answers. Always try to improve yourselves.
If you are facing difficulties in understanding Add Maths, don't scare. Just go and search for help or guidance. This is the best way, and also the faster way to solve your problem. Go for tuition, or seek friends and teachers for help. You can surely understand it after the explanation.
Add Maths might make you frustrated. But always remember, don't give up easily. If you have given up, then you surely can't make it. But if you try, who knows your final SPM result might give you a surprise? Always motivate yourselves. Nothing can be done without trying.