• Fix your goal and start preparing early, as early as after your Class X exam. This will give you an edge over other students.
• Improve your English. Start reading a newspaper daily and make it a regular habit to watch news on TV. Also brush up your Grammar skills.
• Refer to the past years question papers
• Identify your weak subjects and start working on them so that you gain a stronghold.
• Prepare yourself to be calm in the examination hall and answer the questions within the stipulated time.
• As there would be negative marking, it is best to answer only if you are very sure of the answer. Guesses are not going to pay here.
• Spend time on understanding yourself,
• your weak areas and try to strengthen them.
•  start thinking and behaving like an officer.

NDA - National Defence Academy

1. For the exam you don't have to worry. It's MCQ and comes from 11th and 12th and sometimes 10th standard science and maths. Since, you find science difficult use Arihant "Pathfinder for NDA" book, good for NDA preparation and also focus on your english and general aptitude skills.

2. If u clear NDA exam, then your roll no. will appear on UPSC Website and after a few weeks you will get a call letter from respective services. Clearing SSB is a tough task. It's 5 days interview with variety of tasks. If you are not so confident about it, join a training academy which will give you training for SSB. Most people do this to get experience.

3. Important thing toremeber is if you are going first time you have 2-3 percent more chances than when you are going second time. If they have to select between you and a person who has come for second time, they will go for newcomer.So, give your best shot.