You need to constantly monitor what is happening with the market and what coins are worth buying. Some altcoins initially seem promising and even included in the Top 100, but after a while you realize that the team does not fulfill promises or others.
Most projects do a 180 degree change once ICO is over, you can see this immediately in their telegram groups. admins that were present 24/7 suddenly take all the time in the world to get back questions, if they do at all. Would be interesting to hear what other tools you are using to monitor altcoins?