Official DAO proposals are the only way to create enforceable change on the Curve protocol. There are currently two type of votes: parameter and text.
Parameter votes are automatically committed to the DAO three days after they are enacted at the end of the vote. Text proposals are different as they will often necessitate development. For those, it is recommended to discuss with the Curve team to understand feasibility and create a signalling proposal.
To create a new DAO proposal, you need at least 2,500 veCRV (2,500 CRV locked for four years or 10,000 CRV locked for one year).
Visit the Curve DAO: https://dao.curve.fi/dao, select your type of vote and submit it.
Every DAO proposal must be accompanied with a proposal on the Curve governance forum. Visit the proposal section: https://gov.curve.fi/c/proposals/8 and click "New Topic".
You will then be presented with a template to help you present your proposed choices to the community.
After that's done, be sure to engage with members of the community who have questions about your proposal.