You just need a simple Under Graduation Degree from any Stream and then you will have to appear for UPSC CSE examination and if you belong to General category then you will have to get a rank under 200 to become an IPS Officer as top 100 always goes to IAS while some goes for Indian Foreign Service.

I would suggest you to go for BA in Political science or Geography or History so that you can get help in your UPSC preparation.

Hello,
First  of all you need to attain 21 years age, complete your graduation in any discipline from a recognized university or you can also appear in the final year. There's no specific aggregate required in this case.

Coming to preparation part,you can follow the steps mentioned below;

Be acquainted with syllabus,it'll help you know what to read and skip.
Start reading The Hindu on a daily basis, more so focus on editorial part,it will not only increase your knowledge but when it comes to writing answers for mains it'll help you a lot in broadening your perspective.
Start with NCERTs and then move towards standard books,keep resources minimal,read one book many times,instead of three books one time.
Start practicing answer writing in advance,writing mains will be a humongous task.
Go through previous year questions, and mock papers on a regular basis in order to evaluate your progress.