[heliumcraft]

There are different ways, one is simply to do it in the blockchain itself , which is completly transparent so you know exactly what is going on, however this suffers from the flaw that the miners could potentially manipulate it (if the incentive is high enough), some proposals include doing a type of DAO in which participants commit a random value (hashed and revealed later). There are also approaches like the one used by satoshi dice https://www.satoshidice.com/provably-fair/?stage=1