Well, you usually study the site of the coin itself, the white paper, roadmap, etc, and check if it actually makes sense and would look good. Now what "looks good" depends on the person themselves, so that's really up to you to decide imo. After that personally I just browse around random forums and discussions about the token itself. More specifically I try to look up the chances that the project is actually just being shilled or are they completely legit, which in most cases yes, they are being shilled and just hyped around. They can be invested on since they usually pump up in the short term but I mostly look for long term investments.