You can see the project that has at new altcoin, then you can see if the project can be accepted and used in the long term, if then, you can buy and start investing in the coin. Then the second, what you have to pay attention to is an exchange, if in the future the coin will be traded in a large exchange like bittrex, binance and others then you don't have to hesitate to start investing in the coin. Both of these factors can be used as references when you want to invest in a new altcoin.