Do research on coins and see which ones catch your attention. You want to find a coin that catches your attention and has a real use case. Plus you should only invest money you can afford to lose.
With the big number of altcoins and it's increasing, the more we should be very smart in choosing because most of them are scams.
There are a lot of basis in choosing, don't get too comfortable with what you read, you should have a lot of reference because you invest in a coins.