Investing processes are unique to each individual and investment firm. While some rely on investment checklists (I once built one with nearly 80 data points), others might rely on calculating the potential intrinsic value using a discounted cash flow (DCF) model and yet others might focus on the qualitative aspects of the business (management, industry, macro, etc.). Some investors might choose an event-driven strategy like merger arbitrage or stock spinoffs and others might only use technical analysis. I personally use a combination of idea generation from event-driven strategies, building a DCF model when required, peer comparison and writing about the business. Writing helps crystallize my thought process and makes me dive deeper into the qualitative aspects of the business than I would have otherwise.
Once a potential investment is identified through the investment process of your choice, you have to then figure out how it fits into the portfolio.