Increase the required interest rate and use expected dividends. Expected dividends may be increasing or decreasing instead of constant. There are more complicated present value formulas. People don't agree on expected dividends. Many people are employed as analysts who carefully read company reports.
Any news can cause stocks and the market as a whole to change in value.
Many different links to company and academic websites. The Vanguard Group A low-cost leader in the mutual fund industry. A short course on mutual funds From Vanguard. Perhaps the best financial newspaper on the web. The New York Times Not as comprehensive as the Wall Street Journal, but still useful.