I only share that to give you an idea of what can be done. I'm new at this and after watching ya'll who have thousands of followers, I've learned it's more than method. It is what we all like to feel around us-- common courtesy and encouragement. You are all a bunch of caring, encouraging and friendly people, especially the Horror writers, who would think. I bet they don't want anybody to know so, shhh.
Now, for the most part, we are dealing with unseen people, but it still works. People need to know that they matter, that they are noticed and someone cares. How the hell are we suppose to do that on Twitter.
Follow people you like and hope they return the favor.
When people follow you FOLLOW them back whether you like them or not, but not the automated bots. If you look at their post you should be able to tell if you have a real live person there or not. All Retweets and no direct posts is a CLUE. It's not proof but it means something.
After people follow you-for heaven's sake- Thank them. Then take another step and Retweet some of their posts. It's how they'll meet other people.
It also helps to put interesting stuff of your own, pithy quotes, cute puppy and kid pics etc. Start a conversation, butt into one. It's OK.
One thing I found to help make us a friendly community:
Every day or two I put together a post that looks something like this,
I found this gets thrown all over the Twitterverse. People like seeing their name in lights.
What's all this got to do with selling books? Relationships my friend. All sales or at least the good ones thrive on relationship.
Be sincere. Sincerely care
Sell and promote your book, but do it sparingly. People don't want to feel used.
A good book on the basics and some advanced stuff is "Twitter for Writers" by @RayneHall
Lastly- it ain't easy. It's a lot of work. An app like I use @hootsuite helps a lot. You can write a lot of posts and schedule them for the future.
There is a lot more to say... But people hate it when you go long.