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I always read read the whitepaper... Is it something that could be useful in our world of not. Then I join the slack channel (or another chatbchannel) and see how helpfull the people are and if they give fast response to questions. Besides that, i check how the amount of coins is limited or not, and how you could get them, mining? Proof of work? Proof of stake? Proof of investment? Then I check their website, does it look professional? Then I check their wallets, are they easy to use? Is there a possibility for hardware wallet!? Do they have a lite wallet? ...

And these are just some criteria... I also Google the project for news, facts, upcoming events, etc... Good luck!