Pandora has changed their website, PC app, and mobile app so that it is no longer obvious how to add variety to a station. Most instructions online don't apply to these newest versions of their software, or perhaps they're just wrong. Whatever the case, here is correct instructions for how to add variety for each of their applications as of the date of this message. All these instructions assume you're already logged in and that the station you're adding variety to already exists:
You'll probably be presented the last station you were listening to. If so then hit Pause (two vertical bars) to stop the noise, then click on the My Collections link near the upper left hand corner. You'll be presented a list of your stations.
Hover over the album artwork for the station you want to add variety to. A right arrow will appear in it's center, and below it will appear three horizontal dots under the word "More". Clicking on the right arrow will start the station playing, which you don't want, so stay away from it. Clicking on the three horizontal dots will bring up a menu that gives you a choice to "Remove from your collection" or to "Share", so stay away from it too. Click anywhere else on the album artwork.
You'll be presented a webpage that has a "+ Add Variety" link at the top of the list of artists, songs, albums and composers that define that station. Click on this link and you'll be presented a popup where you can enter additional variety.
Same instructions as provided above for the website.
To add variety to a station using the iPhone app:
Bring up the app. It can be downloaded from the app store.
The app will probably present you the station you were last listening to. Hit Pause (two vertical bars) to stop the noise. Click on the down arrow in the upper left hand corner and you'll be presented with a list of all your stations.
Click on the station you want to add variety to.
You'll be presented a page with an information icon in the upper right hand corner (lower case "i" inside a circle). Click on it.
You'll be presented a list of the artists, songs, albums and composers that comprise the variety for your station. Scroll down a bit and in the middle of the list (just where everyone would obviously expect it to be) is the "+ Add Variety" link. Click on it.
You'll be presented a page with a search box where you can enter additional variety.