The easy way to get tickets is via local hackspaces that are somewhat (not necessarily formally) associated to the CCC. There is a ticket contingent for people active in and around the wider chaos community that gets distributed via the hackspaces. They all handle things slightly differently, but the way to get tickets is usually to show up at a hackspace once in a while (or knowing someone who is active there) and getting tickets from there in the presale phase.

The other guaranteed way for tickets is to volunteer enough as an angel at the Congress the year before to get an angel voucher. But you obviously need a ticket for a Congress in the first place do to that.