A COS needs to remove spending authority from Congress and return it to the taxpayer. As presently structured, congress is institutionally incapable of fiscal restraint.
I do not know how to achieve this, but this spending of trillions of dollars we do not have will cost the nation dearly in the future and has to be reversed. Presently, the congress has little or no incentive for fiscal responsibility, and on the contrary, grow their power via spending money and taking us further into debt, be those money sources be tax revenue, borrowing, or printing, the latter two of which are merely taxes by other names.
The best way to restrain spending is to pass/ratify an amendment to the US constitution which requires Congress to keep spending to a level at or below revenue (with an exception provision which would allow temporary deviation in case of national emergency).
States have shown that such a requirement can be done. There is no valid reason (other than the national emergency provision) the federal government cannot do the same.
Congress will not restrain themselves in this area. The people will have to force the issue and a COS is the way to do it, imo.