I don't know how to find out. I use TurboTax so it sort of walked me through that. I know that, for the state of Virginia starting last year, we could either take the "standard" state tax deduction or we could add up our actual state tax that we paid (god imagine keeping track of that!!). Anyway, if you bought a car/boat, etc., it is probably worth doing, but if you didn't, it's better to go with the standard state tax deduction.
If you use any software for state taxes it will walk you through this. If you fill out by hand, it would definitely be in the tax booklet and give the option of doing it both ways. If it's not there then you probably don't have the option of doing it.