What are the Main Strategy of Successful Trader About Stock Market Investment?

The first and most important step is to pick a proper brokerage firm/Demat account. The reasons for my 13 years of experience are here:

The Brokerage based Demat account is best over Bank based Demat account, the reason is you can easily get the answer on your holdings or charges with brokerage firms in a better way, they are trading professionals, and unlike bank professionals, they will have better knowledge.
The Right stock broker choice helps you have a lot of funds that go out of your pocket as Brokerage, supports a total work of 1lakh rupee trade from one firm to other would-be charges from 300Rs to 3500Rs. At the same time if you are cautious in choosing the broker then you can just finish this job in 20Rs.
Zerodha offers a delivery free Demat account, which means any trades you do and hold shares your Demat account for more than 3 busness days will become free of cost, literally zero charges applied even when you make 10lakh work trade, the other firms still keeping their charges here.
Zerodha provides the finest trading platform, which is also the largest used application in India for trading, so Zerodha Kite is ranked as the best in the Industry.
Choosing a firm that also focuses on education, Zerodha varsity does the job satisfactorily, and probably non of the other Indian firms hold this kind of education application.
Zerodha day trading charges are very low, either 20Rd or 0.03% whichever is lower, it means even for a crore worth of trade you will only get the charges of 20Rs.

So, choosing a proper brokerage firm becomes the most important job.