how to create a trending topic

I have this social site am building where users can post and communicate with each other and also search for posts and users, now I want to have AA trending section to see the most trending things around them just like twitter and this are the things I want it to do 1. The trending words should not be things like is, that, the. Any word even if it's the most used shouldn't be trending 2. Update trending things everyday so that it won't be the same everyday 3. Hash tag can be included

Now this is the basic I just want to have an idea of how to do this using PHP, MySQL with fulltext index

And how my database will be structured like if a user post something do I explode the text and store them separately and remove the once I don't want as a trending topic and how do I arrange them

If you need any info please tell m to provide it