"Cleanse the personal income tax system of deductions and lower the marginal rate on a revenue-neutral basis."
Stop taxing corporations' foreign earnings twice, and lower the corporate tax rate to a more competitive 20%.
Simplify the overly complex regulations that make running a business so difficult and costly.
Make monetary policy more predictable by making it rules-based.
Reform (and in the process save) Social Security by adjusting benefits by prices, not wages, and by applying the change only to those under the age of 55. Increase the normal retirement age, and
"when workers reach age 65, stop any payroll deductions and employer contributions to encourage them to stay in the labor force. Their pay will increase and they will be less costly employees. Incentives work."
(As a 65 year old retired person I am painfully aware of the additional 15.3% marginal FICA tax I would face on self-employed income up to $114K, on top of the federal, state, and medicare taxes I'm already paying. It's a powerful disincentive to work.)
Allow insurance companies to offer high-deductible catastrophic healthcare policies, and encourage the use of health-saving accounts. (I note in addition that powerful free-market forces could be unleashed by a simple change to the tax code that allowed everyone, not just employers, to deduct healthcare insurance expenses.)