Hi manoj,
First, have you seen our tips for non-native speakers? We just published some general tips today, and next week we'll be publishing tips on how non-native speakers can approach SC and RC specifically:
https://econgm.at/wycAD8.
For SC problems, here are four skills that can help:
1. Patience - don't jump the gun. For the hardest SC questions, you'll need to go through a few steps before you're ready to answer.
2. Meaning - SC questions are rarely only grammatical. Be sure you understand what the original sentence is trying to convey. This will help you rule out answers that don't make sense or violate the logic or meaning of the sentence.
3. Attention to detail
4. Don't just use your gut or 'ear' to select an answer choice. Try to eliminate incorrect answer choices systematically.
For RC problems, be sure to take notes. Before you get the hang of note-taking, don’t worry about timing. Your timing will improve as you practice. Most people complain about the fact that note-taking takes more time, but in the end, it will actually save you time and make you more precise. Also, read magazines such as the Economist, NY Times, and Financial Times. These type of articles--especially the op-ed sections--are helpful in preparing for the type of passages that appear on the GMAT.
Hope these tips help. Best of luck!
Jessica