In terms of making and passing a proposal there are both social and technical things you’ll need to do.
Technically you will have to send a transaction that contains a json describing which parameter you want to change in which subspace. The Cosmos Hub documentation describes this process and you can also talk to other people who have submitted a proposal for help. The Hypha team who submitted Proposal 63 (including me) would be happy to help on the technical side.
Socially you’ll need buy-in and support from ATOM holders and delegators, since those are the votes that will be required to hit quorum and then pass the proposal itself. I’d recommend actively talking to other validators to get their advice and input on how you can refine the proposal into a form that would be most likely to pass. Once you feel you’ve garnered enough support you’ll be ready to send it on-chain. Some folks who run validators talked about this exact issue in Cryptocito’s recent Splitting ATOM show so you may wish to get in touch with them!
As you continue talking, gaining input, and refining your proposal I’d recommend editing your single top level post and keeping a change-log much like Proposal 63 so that when you’re ready to go on-chain you have the final form of your proposal text ready at hand.
Things you might want to add to your proposal text include rationale, benefits/drawbacks, details about what it would mean to vote YES/NO/VETO/ABSTAIN, and historical precedent such as similar past proposals (Proposal 10 and Proposal 54). Essentially any critical information a voter would need to understand the proposal and make a decision.