If you are like my area, the second installment of my 2017 property taxes is actually not due until March 2018. This is what everyone is saying you might want to pay before the end of the year, if you can. It is not "prepayment" of the 2018 taxes (which is not probably not allowed - but see below). If you itemize in 2017 but won't be in 2018, then you can deduct this early payment in 2017 and get the tax reduction that you won't get for it next year.
I want to do this, but I have an escrow account on my Chase mortgage. I'm giving them a few days to sort things out before calling to see if they can skip making the March tax payment if I request it. I'm good to just pay it myself early, then they could refund the amount to me at my next escrow evaluation in April. We'll see.
For similar reasons, you may want to make your January mortgage payment in the last few days of December, instead of in January.
I did see one article that said the bill may only really exclude prepayment of income taxes, and either doesn't or can't exclude the prepayment of property taxes. But I didn't dig at it and don't know if they were off their rockers or not. They definitely seemed to be swimming against the current on that one compared to everyone else.