Time is taken to write a book, but what a waste of time and money if there is no market for it.
The first step should always be to test the market to see if there is any call for what you want to do. Don't assume anything, you are likely to be wrong.
I was talking to a client and they had a general idea about their book, but they wanted to go down a route, and the competition would be too high. I said this to them, and the book was in the same niche, but on a different topic.
Look at the whole package, and see what you need to do before you jump in with both feet.
Yes, you need to take action, but taking the wrong action will cost you a lot of money and effort.