1. team behind the project?
2. type of blockchain?
3. real-world use-cases?
4. partnerships?
4 points above is what I always see before investing in altcoins and besides that I also see whitepaper so that I know more about the objectives of the project
In my opinion for the point 1 is important to check if there are no scammer DEVS and only good members behind the project. For the point 2 is relative important if you wanna speculate because sometimes marketing is more important than technology when you are only interested to the price