As someone who struggled through a writer's block that lasted for years, I cringe at the memory of what it can do to you. (Retiring out of a toxic job situation has done wonders.) I'm rather a hobbyist writer, so I'm not a good example of how to make a living by writing.
1. I can't come up with whole new story ideas.
What worked for me was mentally playing with the germ of an idea, without pressuring myself to make it into A Novel. And, yes, I played with it for years, but I was dragging myself out of a really dreadful block. After a while, it became a lot of fun and a source of real joy, and I got excited about it and about trying to shape the idea into something I'd enjoy reading.
2. I don't know what should happen next in a current story.
But surely you have an ending in mind. I've written endings before beginnings and then bumbled my way toward them--and then rewritten the ending because it didn't fit. I've also realized that I have a scene in mind that might fit the novel, and written it and then figured out how to get to that scene. And I tend to outline, sort of: jot down stuff that could happen and rearrange them until they sort of make sense. (I looooove how easy it is to revise on a computer.) One thing that helps me is the daydreaming I can do while doing something mindless, even if it's just playing computer solitaire. I can let my mind drift through various possibilities, until I have something that works.
3. I have several radically different directions I could take a current story and am stuck on which direction I should pick.
What might work is writing one and seeing how that goes, and if it goes badly, try another direction. Even when we're not conscious of what we're doing, writers do have a sense of what's working and what's not, and your subconscious will let you know if you've gone in the wrong direction.
4. I know what I want to have in the scene but it's too tough to write, I just don't have the skills or the words.
Ah, the pleasures of revising. Fortunately you don't need to have all the words the first time you write the scene. Getting something down on the screen and then reworking it might work for you. I wrote one of those pivotal, emotional scenes a few months ago and used revising it as a sort of warm-up exercise over the next few weeks. Knowing that I didn't have to achieve perfection right away made it a lot easier to write the foundation of the scene and then rework it until it was what I wanted.
5. I read something good and I just shut down, thinking I'll never be that good.
Ah, but even Homer made errors. And, boy, have I read some terrible sentences written by award-winning writers. I've seen a lot of rough drafts of some fairly prominent writers, and they're ... terrible. (One writer left the climax out of a book in the draft she sent her editor--and it was far from her first book, so you'd think she'd know better.) They don't get that good without a lot of work, and some of them don't get that good without a good editor. And none of them could write the book that you can write, because they're not you; and there is a reader out there wishing she could find a book like the one you have in mind.
Wow--I wrote a novel here! But there are so many ways we can sabotage ourselves, and I've managed to explore just about every one of them.
