There are only a few basic hard and fast rules to writing.
I once read that writing is like eating an elephant. If you look at how much is ahead it can stop you from even beginning. But if you just take it one bite at a time, you’ll eventually get there. How fast will depend on how big of bites you take.
You have the idea and subject and whether it’s fiction or non-fiction much of the process itself is the same. Start with a basic outline. If you have timelines that bounce around, get those nailed down or they’ll trip you up. This can cost you a lot of editing time and I don’t know about you but editing is my least favorite thing. But I have found that doing the line by line and page by page editing as you go is a lot easier than editing the whole elephant at the end.
If it’s fiction, make sure your main characters are hashed out. It’s important to give them a life and some backstory. Even if you don’t use the history about them it makes your writing fuller.
One of the other very important rules is to commit to a daily amount of time. I write 4 hours a day, usually in the morning while everyone is gone. Occasionally I can’t write in the morning so I will do it later, even if it’s after everyone is asleep.
If it’s non-fiction writing, then make sure to do your research. Misinformation will cost you credibility.
Writing is dedication, dedication, dedication.