First you have to determine in advance how many participants you want to be given tokens, but if I think a total supply of 100 million it will be very difficult to attract people if you only give 5% of the total supply, at least 10% will be better
it's not all should be depends on the total allocation for the airdrop, mostly of companies were allocating a small percentage from the total tokens to be distributed through use airdrop method.
This must be a small amount of tokens to avoid the dump.