My best results from an airdrop so far was from optimism project and resulted in $800. If only I hadn't dumped them on the market immediately, in half a year I would have had $5k lol.
If you are new, I suggest doing airdrops that don't require you to invest money. Paying for gas is ok, as long as gas is not in Eth, cause that could be an arm and a leg.
Testnets are a safe bet. For example right now I am participating in the Prom Testnet Campaign. Each day I go to their website, claim some test tokens from the faucet twice a day and them spend them doing various testnet activities: 2 transactions to friends, minting NFTs, minting tokens. Some projects don't tell you how many transactions you need, so it is advisable to do a minimum of 10-30. But with Prom you have a dashboard which tells you what exactly you need to do and how many times a day, so its pretty convenient and easy. Best part - 0 expenses from my account, only daily participation is required. The prize pool will be 1 million $PROM to be devided in proportion to points that the winners received. There are certain specifics of course, that vary from project to project. For example with Prom - these will be community governance tokens. Which means you can't sell them, but you can use them to vote and earn money by voting. So I always advise to read the rules, whitepaper and ask fellow users for advice. Oh, and don't waste your time doing stuff for projects that have not openly confirmed that they WILL have an airdrop. Unless you really know what you are doing.