Before buying a stock, there are mainly two steps to do. First is to follow the company's news and see if there are any positive news that were released. Second is to perform a valuation, either bottoms-up or top-down valuation.
For new investors, can try the ratio method (e.g. P/E or EV/EBITDA multiple). In this method, check the average multiple of the peers in the same industry. Then calculate the target share price using forecast earnings. If current share price is lower than target share price, can consider to buy.
The decision to sell a stock depends on whether the share price has reached the target share price.