There is no accurate measure of how profitable the project will be. Demand vs supply dictates everything. But if the project is really good and people start to recognize it, then there is a high chance that it can be profitable if you are an early adopter.
Take an example of Bitcoin; it took some years for it to gain value, the main player was the rise in its demand over the years.

So here are the key aspects;

• What problem does the project tackle using the blockchain?
• What blockchain based solution does it have in place?
• How unique is the solution offered from other solutions provided by other projects before
• Is the solution offered feasible?
• How experienced are the team members when it comes to the blockchain technology
• Is the project adoptable?
• Is the project in line with the regulations?
  e.t.c
  

Note: Am emphasizing blockchain technology in my points because it's the newest kid on the block and would love to see it prosper

That said, There are so many articles online which could help you to identify if a project is just scam or legit. I will share a few links here, you can do more research online.
- 10 Ways How to Spot a Scam ICO
- How to Identify Cryptocurrency and ICO Scams
- 10 keys for evaluating Initial Coin Offering (ICO) investments

You can also visit the scam accusations board and you get to see and learn how some members identify scam projects