Probably depends on the genre you like to write and honestly I've JUST gotten into them.

Today I'm picking a copy of "Writing the breakout novel" from the library that Ally mentioned, because I've heard that one talked about quite a bit on this site, but I have to say even with it's seemingly bad reviews I really enjoyed the sci-fi/fantasy how to by David Gerrold called "Worlds of Wonder How to Write Science Fiction & Fantasy." It wasn't exactly what I was looking for but I got TONS of inspiration from it and got over my writing block very quickly and got me writing from prompts and exploring myself and my writing by DOING and trying different things. And learned a LOT in the process.

There are so many how to books out there, it's overwhelming, but I think if one makes you want to sit down and write and try out its techniques then you've got a winner. So keep experimenting and start with your local library so you don't drain the bank account!! Lol

Good Luck!!

Darleen
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“The scariest moment is always just before you start.”
― Stephen King, On Writing