The best attitude to cultivate for writing is: "don't care", that is, complete and utter nonchalance.
If I'm writing for a client and I desperately want to write well, I take that as an alarm, a warning. I know that whatever I write with this attitude will be garbage.
Therefore, I've trained myself. It's reverse psychology. I convince myself that I don't care what I write, I'm happy to write junk. In fact, I DEMAND that I write junk.
With this attitude, it takes ten to 15 minutes for me to become engrossed in what I'm writing. As soon as I start to have fun, I know I'm writing well.
How do you get to that "don't care" state? Tell yourself that you can destroy your writing if you're not happy with it. It's true. You can. Then tell yourself just to have fun, and to enjoy your creativity.