Hyy Rajam 

For Ntse preparation and specifically stage 1, follow these guidelines 

• A - Just buy your State Board Social Sciences book and read History and Geography very seriously. Moreover start practicing MAT on daily basis. Solve previous year MAT papers of other states. That's all. No need of RS Aggarwal (MAT one) as of now. Just make sure you are not overconfident and maintain at least 16/20 marks in Maths and 35/40 marks in science.              
• B - You now may have realised that you have really awesome competitors (A) and it would be a challenge to beat them. The State Board Social Sciences book and MAT strategy is the same for all (even C). However you should work on your Maths and Science part. For this you should start by clearing your basics. For Science, read books by MTGand solve them. For Maths, solve the good questions of RD Sharma(normally the solved examples and HOTS. The Exercises usually don't involve new concept).                                                              
• C - Just forget about A and B. Get the State Board Social Sciences books and read. Just read. Highlight important points. Solve back exercises. You must have realised that beating A and B for Science and Maths is difficult. Wreck those A guys with your SST knowledge. Give extreme emphasis on MAT. Target at least 45+/50 in MAT. Follow the same strategy for Maths and Science as B and make sure you are scoring at least 13/20 in Maths and 30–33/40 in Science.

Hello Rajam, Thanks for approaching us to prepare for NTSE stay true to NCERT. Especially for SST, read the class 9-10 books thoroughly. You'll surely get full marks in SST by doing this much. And that's quite significant.

Practice MAT from the RD Sharma MAT book.

Daily maths practice from standard books like RS Agarwal and RD Sharma is enough.

For science, again, stay true to NCERT and then study MTG Foundation Series books of class 9–10 of PCB. That'll do loads of help

A final touch can be MTG NTSE Explorer

Best of Luck.