I think in this day and age it has changed some what... Back when altcoins first started exploding at the end of 2013, you could invest in pretty much any new coin and make a quick buck.

Now there are so many different ideas out there, different coins that all actually have potential, that it's difficult to choose which ones to invest in. There are many coins with good ideas, now it's really important to check the credentials of the team and make sure the idea behind the coin is sound, that they have an achievement roadmap etc.
Don't buy acoin just because it's 400th+ on coinmarketcap and could increase... does it have good technology behind it? Who's driving the development? etc

If I were to invest in any at the moment they'd be ones that have been around a while and are at least top 100 market cap. Buying/selling low volume coins is also a complete hassle. Even if it goes up 100x it doesn't matter if no one is buying!