Depends upon the time frame you're under the gun to overcome the issue.
For writers that "just start" a story and have no idea where they're going or how they're going to get there writer's blocks will be an ever present specter to stymie their progress.
I'd never advocate this approach. It's a recipe for a soul grinding catastrophe.
"I'm just going to wake up in the morning, take off all my clothes, and run naked through the streets. See how that turns out."
Umm... yeah. Don't do that.
For those writers that have nothing at the moment burning a hole in their head but "think" they "should" be doing something I'd suggest:
http://www.indietalk.com/showthread.php?p=186753#post186753
http://www.indietalk.com/showthread.php?p=196432#post196432
For a writer with an immediate deadline of a few hours or days go back and re-outline the whole story, connect your dots how A leads to B, B to C, and so forth.
Do it on paper/computer.
Not in your head. There's too much sh!t jammed in there already, which is the nature of the problem.
By stepping back a moment you'll likely "see" some workaround that wasn't apparent before.
You really don't have time for lollygagging, so "Chop! Chop!" get your a$$ to work.
For a writer with weeks to months to produce product then take the luxury of a deep fall back.
Get away from the material.
Revisit a dropped interest, go wander the mall/Home Depot/marina/cat house/another writing project.
Just get the away from what you're working on overtly so that your subconscious can get some breathing room and working space to rearrange some pieces which are jammed tight together and going nowhere.
Ever poured crumbly material through a funnel only to have it jam in the neck?
Same thing, except you can't use a stick to poke and jab inside your mind.
How about you quit pouring too much material through a fixed port?
Jathink?!
If you'd physically outline a project beforehand, breaking it down into a list of discrete quanta of goals, like construction directions, you can avoid writers block altogether.
GL!