1. General Studies Paper-I is bound to be very tough. If you can get 100 marks out of 200 you are on right track. Many students lost out last year because though could attempt 50 questions correctly, yet they made wild guesses which reduced their marks. Therefore, in this paper it is better to make only educated guesses. Do not refrain from guessing totally this will reduce your marks, but guess only when you know at least 60% of the answer.
2. Paper-II is where you have to score. You should be able to get at least 130 marks out of 200. Ideally, get your marks in the English Comprehension and the basic numeracy sections. Also, questions on decision making did not have Negative Marking last year. In case there is no negative marking you can make the guesses. Because you will not loose out.
3. There are no separate cut-off for each paper. The combined cut-off is taken. This was given by UPSC in an answer to a question filed by a student under the Right to Information Act. Therefore, do not fall a victim to any rumours that there is an individual cutoff for each paper. However remember U.P.S.C has every right to change the norms.
See previous article for comprehensive preparation strategy:
Prelims Exam Structure and Syllabus
Why Negative Marking?
Strategy for Paper 1
Strategy for Paper 2