Since I'm highly in tune with the Cosmos ecosystem, I've followed the right YouTubers, am in lots of Discord groups for upcoming projects, and also search around for more clues on the web that ultimately lead me to news/rumors on Reddit or Twitter. I don't really post about them specifically, but I've mentioned the general flurry of them on the Cosmos ecosystem a few times. There are a few general airdrop tracking websites you can explore and see if you may already be qualified for. An example is: https://airdrops.io/. There's also a website where you can put your ETH addresses in to see if you've potentially missed any free money in the past. https://earni.fi/

Basically, if you proactively search on a regular basis, they're pretty easy to find and prepare for in time as some take some setup, like setting up XRP trustlines. Many airdrops have airdrop calculator sites where you can paste your addresses in and see if you made the snapshots/how much you'll get when it's ready.

Here's a tip for Terra Luna: https://terra.smartstake.io/airdrops.