The most effective way to cure writer's block is to write. The first thought that springs to mind after hearing this is: how to do this when you have it, isn't it a catch 22?
Yes, but mostly--no.
Here is why. If you can just start writing your mind will begin engaging in ways you really hadn't thought possible. You will begin to write and some of it will be garbage, granted. However, much of it will either be exactly what you were looking for or it will be fodder for some other project. Either way you win.
You will have successfully beaten the writer's block and if you can continue to do so you will be free from this affliction. Sometimes (in rather strange circles) this virus is mistakenly referred to as a social disease, as it seems to strike when a writer has been invited to go out with their friends. If you find you really are stuck, perhaps try going out with your friends and come back refreshed from taking time to live.
Another strategy, if you just simply feel too guilty about not writing to go out, is to live vicariously though other characters. Read a good book that you have been putting off reading because you really needed to write those next few pages. Yet, you are staring at a blank page and nothing is what springs to mind. This is your inner five year old wanting a story told to him or her. Oblige the little bookworm so you can get back to doing what you do best, being creative.
Some writers are so full of words they will not face writer's block, or least they claim they haven't. Don't let them fool you, they just kept writing and maybe most of it was gobbledygook. No matter. They still win. Once you can get past the empty page you can start getting back into the rhythm of really writing and, just as muscles remember after they have done something in repetition, your writing muscles will engage.
These are some keys on the writers craft I have picked up along the way, they all boil down to one rule--just write.