I don't actually believe in "writer's block." I think we go through periods when it's harder to write, when the words don't flow--I call it "writing through mud." My answer is: write anyway. Write even if you know you'll have to toss it all and replace it in editing. Eventually, you will write your way out the other side and things will start to flow again.
It's hard to stay motivated when that happens, but writing something--even if it's terrible--is the best way to get back to writing well.