"Let others pride themselves about how many pages they've written; I'd rather boast about the ones I've read." Jorge Luis Borges
I don't agree with those who say that we all have to write every single day. I do think it is important to write regularly, but writing every day when you have nothing to say is pointless.
I only write when I have something to say, which happens to be almost every day. The same applies to blogging. I feel compelled to post if I believe that what I write is of relevance. (Many times I write posts that I never have the courage to post).
Writing goes hand in hand with living. It is ingrained in my thoughts, my actions, the way I experience life.
This does not mean that I always know where I am going every time I sit to write. Sometimes a first sentence can be the beginning of a story, a journey into the unkown. There are two important things I can recommend:
1) When you have an idea, you need to put it on paper (or on the screen) and let it linger in your mind. Carrying a note-book will make your writing life easier.
2) Embrace uncertainty. You can't predict if the outcome will be acceptable. You need to trust your motivation and your intuition without fretting over the outcome. You need to push through the boundaries of uncertainty.
This is not easy because since a very early age we are taught that it is not okay to make mistakes. However, whenever you are creating something you need to give yourself the freedom to do it. Here's an excellent article on this:
Why are we so afraid of creativity? from Scientific American.
How often do you write?