Some of my ideas were shot down by Lucasfilm because they stepped on territory that has been reserved for the movies. I didn't have a problem with that.
I've learned that I get blocked when my subconscious mind is telling me that I've taken the work in a wrong direction, and that once I start listening to what my subconscious is trying to tell me, I can work out the problem and get moving again.
It's hard to generalize, because they're all different. When I started, I decided to take as much advantage as I could of the freedom offered by the SF field.
That's why editors and publishers will never be obsolete: a reader wants someone with taste and authority to point them in the direction of the good stuff, and to keep the awful stuff away from their door.
The Internet offers an interesting combination of advertising and community by participating in the community you can become an advertisement for yourself.