You have exactly 4 months in this year, 12 months in 2019 and 4–5 months in the 2020 before the prelims.
Read the topic-wise divided syllabus here on my website.
Study the previous year question papers. You can refer the last 10–11 years papers for the prelims & 5–7 years papers for the mains. Try to understand the pattern, how the questions has been forming since last few years, how is trend going on, and what is the exact the demand of the UPSC. If you are not going to do this, then your situation will be something like this.
Next Start reading the NCERTs from July, 2018. Almost 44–45 textbooks are there. Cover 3–5 chapters on a daily basis. It will not take more than 6 monthsin general. In 2018, your NCERTs must be finished and you must come into the flow of current affairs as well.
Make the notes from the NCERTs, at least do it for the 6th to 10th class.
Decide your optional also in the entire 6 months of 2018. And 6 months are enough to take decision. Same mechanism will be applied here, read the syllabus and PYQs.
For the current affairs, read the Hindu or the Indian Express. You will find both Read more