History optional is useful because of the following reasons.
- It is a very interesting subject and hence can be fun to read and re-read during the course of preparation. Even the technical aspects of the subject and the debates that accompany the different schools of thought are so much engrossing.
- History gives you a better appreciation of daily news that you come across. Thus you will be able to better place the conflict in Palestine, the oppression of the blacks in USA, the historical context of US-Russia relations, Kashmir issue etc.
- History is extremely scoring for well prepared candidates, and also manages to give you moderate marks even if you haven’t prepared that exhaustively.
- History is also very useful for GS paper I and some parts of GS II and GS III. MY GS I mark is 109, which would not have been possible without my history background.
- It is very logical and the arguments of different sides on the same issue will appeal to your logic and reasoning.
The easiest way to start preparing for History optional is to have a look at the past years question papers, and read up on one or two topics that are covered. Once you are done with that, revisit those questions and see if you are able to answer them as expected in history optional paper. I think it is best that you get it corrected by someone from history background. Now if you feel confident that you have an aptitude for history, then start with the standard text books.
I have listed elsewhere, the standard history text books that you can refer. You should also give sufficient attention to Maps section. Ignoring Maps is a mistake that every newcomer in history does. Keep sometime everyday to study maps.
It would also help if you can find a history test series in your town, or if you can attempt all past questions on your own.