To double the salary is not enough to earn money, smart investment is equally important for this. You can start regular investment in SIP, RD and mutual funds. Special schemes and offers are also available in many banks and insurance companies for teachers. Remember, small investment can make large funds over time.
Disclaimer: This article is only for general information and educational purposes. The earnings from the methods mentioned in it will depend on skills, time and situation. Be sure to consult your financial advisor before starting any investment or new earnings.