Why do you use tags?
Choose from most used tags
WordPress makes this easy on you.
When you want to tag your post, you can use the link
"Choose from the most used tags"
You can easily see which tags you have used before, and which posts you can link together with the appropriate tag. That, when people click your tag, they will be lead to the tag archive page and see the related posts on your website. And also handy for Google, Bing and Yahoo to see which posts are connected.