Selection of optional subjects is a bit tricky job that’s why lots of aspirants get confused but I would like you to get relaxed and make this important decision with few things in your mind.
First thing that you must consider is your aptitude for the subject in question. You might find one subject scoring but if you do not have aptitude for that subject, you will never be able to earn good marks. The next thing that you should consider is your interest. In my view interest is the primary thing that can help you sail smoothly while preparing and appearing in actual examination. Once you have these things in your mind, you are ready to go for selection of subjects. Now, you need to get hold of the complete list of optional subjects, next, jot down those subjects that you find interesting and you have aptitude for and lastly, have a look at the past papers of the subjects of you noted down, if you find it easy to deal the questions in past papers, choose that subject and start preparing.