Every airdrop has a different set of rules. We suggest you make a Bitcointalk forum account to be able to apply for the airdrops that require contacting a team member (usually PM). Ethereum Dark airdrop is a good example for this format. Every person that wanted to apply for this ETHd airdrop had to PM the developer with his ETHd address to get the tokens. “Newbies” on the forum are often rejected for new airdrops, so we suggest you post once in a while to get a higher rank.
Some new airdrops require retweets on Twitter, usually you need a minimum amount of followers. Make sure you have active social media accounts to be eligible for these free crypto tokens.
Check your wallets regularly to see if you received surprise airdrops. Platforms like Waves or Komodo have delivered airdrops for Waves or Komodo holders without any announcement.
If you are an investor holding a diverse portfolio of coins you are likely to be receiving more and more free crypto as this concept keeps gaining popularity.