you must look into a lot of aspects but the main ones are
1) team (real or not, investigate)
2) whitepaper
3) product (finished or not)
4) use case for product
5) cap and token sale details
I am sure there are few more but those are most important
It think this answer good. But I can advise to pay attention to the financing scheme. The money goes directly to the creators of ico or the funding comes gradually, as the fulfillment of the conditions of the contract.