For contributing guidelines see the Project Liberty Contributing Guidelines.
A DIP is any update that would materially change the DSNP specification, as opposed to non-material changes, like fixing spelling errors. There is a pre-configured issue template for creating DIPs as part of the DSNP Specification repository.
As the DSNP protocol matures, we will create a DIP governance and approval process that's appropriate to the evolving needs of the community, following well-established open source development practices. For now, we simply discuss the merits of the suggested change and approve or disapprove based on a rough consensus.