A common tax planning practice is to make year-end prepayments of state and local taxes that would be due the next year anyway. Such payments will reduce the amount of regular tax you’ll owe for the current year.
However, pre-paying state and local tax won’t reduce your alternative minimum tax (AMT). If you reduce your regular tax bill by too large an amount, you’ll wind up paying the AMT. Once you’re subject to the AMT, you’ll get no benefit from these pre-payments.
Your best strategy, therefore, is to ask your tax advisor how much you can pre-pay this year before reaching the cross-over point: the point after which you’d get no benefit. Similar rules apply to miscellaneous itemized deductions so you should proceed cautiously before making year-end prepayments of investment and legal fees, tax preparation fees, etc.