Start with the assumption it is a scam and then move through the stages to make yourself believe it is not.
Team members with relevant blockchain AND sector experience ?
Do you like / believe the whitepaper ?
Backed by known entities or people - i.e. not celebrities and not known crypto people, but relevant real world and business people.
Avoid the hyped projects.
Check that the structure is not based on team money extraction - i.e. for example ICOs where tokens are issued to the team without considering the amount raised (such as Powerledger).
The best at the moment for all of the above is Prosume Energy.
Check the WP, team members with unbelievable knowledge, Ernst and Young on the advisory board as well as sovereign wealth fund advisor.
Existing project.