I have seen many different ways it is done, not 1 single way.

For example :

DeepOnion - Every week, you need to meet the minimum criteria and be a Jr. Member or better on Bitcoin talk, post on both forums etc..
TRX - Was just a random drop in to different accounts.
SingularDTV - they did one where they sent a different token to people who were holding SNGL and it was just a decision they made, no previous info.

Have a read in to specific coins you want and see if they offer it, otherwise just support projects you like by owning tokens and then see what happens.