You must look for the coins potential if it will be able to sustain its needs for a long time. Also check the backgrouns of the developers if they have been part of some successful project for you to check if they are legit or scam. Also check the current market movement if the value of it is good to invest to or not.
Well, checking the people or names behind those projects are the first or the investors should prioritize. That is the most important before you look on how promising the project is. Read the whitepaper, there are a lot of ways to determine if a project is legit or not but there are some that is hard to identify.