How do you decide when to buy/sell a stock?

It is broadly classified into two groups:
1) trader
2) investor

As a trader, your objective is to have a quick win by buying or selling a stock in a short time frame quickly. Therefore, using TA and news as a tool to execute the buy/sell decision.

While for investors, you intend to hold a stock for the mid to long term, depending on the company prospects now and future. You will do your diligence to study the company profile based on SWAT strategy to decide if to buy or sell. You ignore the market noise as you believe the company's value will appreciate in the long run.