I like to analyse altcoins like an angel investors would analyse an early stage startup before a seed investment. It's also important to understand what the token/coin represents in their business model, since this is metaphorically your contract in terms of ROI.
So, basically you look for good startups. Team, background, market, value proposition, etc. Plenty of awesome materials in the internet about this.
Also, there are some basic sources of information that you always might want to look for:
_Official subreddit or place where the community is
A good topic is where a good discussions is, so always look for the comments and not only the topic itself. Find where the devs/team are and follow their posts.
_Official communication channels
Slack, Twitter, Telegram, Discord
_Official documentations
Whitepaper and Roadmap
_Official Github
The cherry on the cake, if you know what the heck is in there.
edit: Edited to add some sources of information.