Like all writers, I wish writer's block never happened! But it does, and since I don't have magic to make it simply disappear, I've discovered a few things which help me get over the inevitable slump.
Since I'm currently writing three separate series (I know, I'm insane) one thing I'll do is stop whatever I'm working on whatever is giving me trouble, move to a different piece, and thank my lucky stars I can switch between three worlds so easily.
Something else I do is work on promotion or administrative tasks to let my brain sort through the whirlwind of thoughts. I'll focus on something entirely different for an hour or so and then go back to writing. So far, it's been pretty successful.
I also find that walking away from work completely for even fifteen minutes helps tremendously. Doing chores around the house, reading, playing my cello, and (don't laugh) taking a shower gives me the mental break I need. When I walk away completely, I'm not forcing anything and the words/thoughts just come.
....and when all else is lost, I have a neat Jameson :)