Disclaimer: These apply to me and my writing quirks. They may not apply to you and in fact it's possible that you need to do the opposite in some cases.
1. Write the first draft as though you are fleeing from Sodom and Gomorrah, i.e. just keep going, don't look back! The resulting draft will be neither as brilliant as one hopes nor as horrid as one fears. It will have good bits and bad bits, but can be revised. Beware the Endless Revision Loop!
2. Neither writing a synopsis upfront with a detailed plan of the story nor "writing to explore" works. Aim for the Middle WayTM, that is have a general idea of the overall arc of the story, but leave the detail to be discovered en route.
3. I need encouragement; I need to feel that someone wants me to finish the novel. But if I let people read the novel, I either want to go back and change the things they comment on or, if they praise it, I freeze with performance anxiety because I'm convinced that the next bit will not live up to the part they just read. Posting snippets of the good bits to LJ lets people know I'm progressing without the danger of falling into the Endless Revision Loop or succumbing to writer's block.
4. Never, having let someone read the opening of a novel, continue to write the rest as though the changes I need to make have already been made. Therein lies madness. Just don't let anyone read a novel until it's finished. It's much easier for everyone concerned.
5. Writing short stories is a waste of time. So many people are so much better at it that it's just not worth trying to compete. Far fewer people have the sheer stamina required to finish a 100,000 word novel and then go through it several more times while revising. I can do this, others can't. Having said that, short stories can be used to try out something new, e.g. omniscient viewpoint.
6. I should play to my strengths. Rather than constantly struggling to keep the tone of a story serious, write comedy! Leave angst to the youngsters. They do it so much better.
7, Having said that, it's good for me to push myself into new and unfamiliar areas. For example take a poetry course.
8. If I get stuck, try going back to writing by hand, with a fountain pen.
9. Whilst writing rituals can help to get the writing flowing when I'm writing at home, I can actually write almost anywhere including cafes and trains. In fact long train journeys are good for writing.
10. I must not overplan scenes in my head. Get words down on paper as soon as I know what's happening. However sketchy they are, they can be worked up into something better.
There are more, but I think those are the most important ones.
Off now to pick some more nits out of the final draft...