I think it’s good idea to see around how other DAOs have solved this, so I think we just collect/look at some Improvement Proposal of other DAO first.
Curve (quite loose): Proposals How-to - Proposals - Curve.fi Governance
GnosisDao: (very structured) : README: GnosisDAO Governance Process - GnosisDAO - Gnosis
Uniswap: (structured) Community Governance Process - Governance-Meta - Uniswap Governance
Sushiswap: (quite loose) About the Proposals & Proposal How-To - Proposals - SushiSwap
Balancer (none found) Proposals - Balancer
PrimeDao: Create Your First Proposal - PrimeDAO Docs
The mother ship: https://eips.ethereum.org/ / EIP-1: EIP Purpose and Guidelines
This short research showed me that this can be done in very different ways 
