Honestly, I don't join in any airdrops actually. Because , there are other airdrops once you fill up their form they are asking for your private key which is indicates that they can hack your wallet in your MEW, were it is not good anyway. And most of airdrops was a piece of shit coins.
that is obviously a scam and not an airdrop at all. me myself have involved in many airdrops in the past because im eagerly want to earn a profit to them and i think that i could be wealthy by joining 10 to 20 airdrops a day but hell no, the price of their tokens/coins are still pretty low and dont even pump after some months or two just by holding them patiently. airdrops dont requires you to expose your private key publicaly because private key is verry important and acts like a password to unluck or acces your account.
with hugely growing cryptocommunity we have now, i guess the main thing about airdrops is to get into the limited number of participants in time. so if you want to make moneny on airdrops be ready to keep an eye on all aggregating sites or telegram groups 24/7.
yes most airdrops have a set limit for required participants to join but if you miss the their airdrops , you can then still wait because most of them had a certain round or phase that will be held again on the specified time and date. joining their groups and following their social media accounts is also a good way to track them.