Start with a Total addressable market (TAM) * share of TAM you can get in next 3-5 years *confidence level *Revenue per user per year * 3-5 years.
In the RICE framework, you would divide TAM * Share of TAM (influence) * Confience/ Effort to then help prioritize. (Desc)
Calculating Share of TAM you can get in next 3-5 years is a art more than science. Do a SWOT analysis for yourself, incumbents in the market, if any and emerging players. Also keep in mind that market/users may not always be ready to adopt. So factor in the barrier to adoption/switching costs.
Confidence level is based on your ablity to execute and deliver results- ship great products, great customer support, sales channels, marketing (even if lo-budget). Do you have the right team to get this done? Is the technology there yet? Are there high risk dependencies?