True, as others pointed out, it is helpful to understand what motivates each of your sales people.
However in addition, as you develop your plan, be clear on: - your goals (lead generation, acquire/build market share, increase revenue, or customer retention etc.)
- what your target market may yield - you don't want to offer incentives that over generate then have to back pedal later, so consider if you need some caps.
- scalability; ensure the company can actually deliver on the sales generated.
- frequency to pay out; largely depends on the goal
- how you will measure results; keep it fair; make sure measurement aligns with business results.
- visibility to the metrics - nothing loses sales people faster than the perception of being cheated on commissions or bonuses.
- flexibility - as business fluctuates ensure your plan does too
- churn - very clearly state how people get paid if/when they leave.
Different roles on the team may require somewhat different incentives to carry out the right behaviour (ie. find new customers, sell more X than Y, deliver excellent service, sell widgets, retain customer) consider if you want some team goals as well as individual, depending on what exactly you are trying to grow.
A good plan 'incents' the correct behaviour of your team to go after the right type of business/qualified customer/lead to accomplish your business goals.
Lastly, consider how you will modify plans or implement interim spiff programs as the company/business grows, so you can build expectation with the team up front on how you might implement a change in future.
I have helped leaders think through different components of incentive plans, I don't do the math but I know how to think it through. Happy to help.