1. Invest for long term. 
2. Learn and understand about market fluctuations. 
3. Start with small investments and in staggered way.
4. Stay away from stock market if you think stock market is a place for short term profit booking or gambling.  
5. Invest only that much amount which you can afford to lose. 
6. Do not invest in the stock market for the short term for the sake of earning profit.
7. If you are making a long-term investment with a purpose, do not wait for the right time to enter the market.
8. Your investment objective must be right to keep money in the stock market. ‘Getting rich quick’ and ‘earning money in the short run’  are not the right kind of goals.
9. Don’t invest based on stockbroker’s or stock trader’s recommendations. Be sure to research the company or stock before investing.
10. If you are new to stock market investing, invest in blue-chip stocks or shares of a large companies.
11. Keep learning parallel to the investment. 
12. Learning more about the stock market gives you an idea of ​​how the market reacts to different economic/political/weather conditions, news and affairs etc.
13. Before investing, understand that the stock market is not a simple ride, but it could be an exciting ride if you are ready to learn about the ups and downs.
14. The stock market, as they say, is a bumpy ride, sometimes the market goes up or sometimes the market goes down suddenly. Therefore, make sure that you can bear the risk before investing.
15. Stock market risk is inherent. The risk of the stock market cannot be separated, But one can reduce the market risk through different strategies, asset allocation and diversification.
16. Don’t try to fix market time. There is no perfect time to start investing in the market. Start early and invest for long term.
17. Ups and downs are the part of market cycle. Don’t try to take advantage of this cycle to earn money quickly. That’s why Warren Buffett recommends investing for the long term.
18. Avoid listening to stock market shows on TV through popular channels and don’t invest in their recommendations. They all recommend it on a general basis. Investors needs to filter the general information they receive from news, brokers, traders and see if it is right and suitable to them. 
19. Stop copying others decisions. Rather consider your own risks and goals to understand how and where to invest.
20. Following the fundamental analysis of a stock company is the best way to choose a good stock. Diversify your investments in the stock market as well. Invest in different types of stocks of the company like IT, pharma, bank, health, goods and services companies, mobile companies etc. so that you can take advantage of all the markets and reduce the risk. I hope these issues help you build your confidence and help you ‘make decisions’.

Note:- Above article based on one of my Quora Answer.