Depending on your interests you can choose a hard ware or software line. In hardware, telecom, IC design, circuitry are useful options that will go with your area. I guess if you start concentrating more on studies right now will be useful. For earning, you may take up 12th Maths, Physics and Chemistry crash courses. Visit the nearest coaching center and look for vacancies. Alternatively, meet some students outside the coaching centers. Ask the students some basic yet tricky questions. Their focus is max marks in 12th. They may get impressed and take some additional special classes from you. Since you are studying engineering, which perhaps may be their dream too, you will get some students. Keep numbers low so that you do not loose focus. You aim is not immediate short-term gain. You are working for long term gain, which can be built only when you have completed your studies.

Your counsel.