When you have your following, you could create lists of people, or groups. It is not mandatory, but it may help you when you want to direct your tweets at a specific group of people.

Here's an example of lists that are aimed at authors and author retweeters

You can create a group for affiliate marketers, readers, bloggers, baby boomers, and add people there accordingly. Then, when you want to add one of those groups to a tweet, just type # and the name of the group, and all its members will see your tweet.

To create a list, simply click on the button as indicated in the screenshot.

After that a new window will pop up, and you fill in the name of the list, write a brief description, and mark is as public or private.

To add someone to a list, simply go to their profile. In the top right corner of their profile you will see a button with three dots. Click there and a menu will appear. Select "add/delete from list"

(sorry, as you can see I don't draw the finest arrows in Paint) ;-) but at least I hope that the explanation is clear.