The first step is to organise who you want involved in the Secret Santa. The easiest way is to straight out ask your friends who wants to be involved whether it's face to face, via personal messaging or starting a topic in a discussion forum.
Make sure to make a deadline for people to say they want to participate. Also lay out rules as to how much each person will be spending on the present they must buy and the latest possible date that the present has to be sent by.
