Pandora currently has 1 million songs in it's catalog and adds about 10,000 songs a month. Pandora's algorithm is excellent but it could really use 1 billion to work properly.
Pandora radio works best when you chose one song as a station seed(never chose an artist as the algorithm is based on songs not on singers). Even if you like all of Taylor Swift's songs you probably like them because of her vocal timbre not because of all the songs themselves. So if you chose Taylor Swift, Pandora's algorithm will pick out songs that have qualities resembeling those songs but you may not like all those songs because they are sung by singers who don't have Taylor Swifts vocal timbre.
Ideally, you want to pick a perfect song that has all the elements of a song you like so when the algorithm choses songs it picks songs with a subset of attributes of songs you like. If you hate long musical interludes don't pick a seed song with a long musical interlude just because the other parts of the song make up for it.
Chosing a single song works best. Use a thumbs up like this: Do you want to hear this song more frequently than other songs on the station? If yes, then thumbs it up. If you revise your opinion of a song then thumbs it down and thumbs it up again so it goes to the top of the thumbs up track list and then click the x button.
If you are okay with hearing a song once. Then don't do anything and the next time the song comes up click the button "I'm tired of this song". If you've heard the song too many times before on the radio click the "I'm tired of this song" button.
If you wish you hadn't heard the song even once then click the thumbs down button. The problem with the thumbs down button is that if you click two thumbs down for a single artist it bans that artist for the station. This is a problem as sometimes artists have featured artists that can change your song. Let's say you hate John Mayer but love Taylor Swift. If you ban John Mayer, then you also ban Half of My Heart which features Taylor Swift on vocals.
If you create a station this way, you'll probably get sick of the station in about two weeks. You can extend the life of the station by continuing to refine your station by deleting the thumbs up of the weaker songs and by chosing "I'm tired of this song" to force the algorithm to present you with new songs.
What you can either do is create a new station based on another "Perfect Song" or you can add variety to create new stations.
If you chose to create a new station the advantage is that you can return to old stations after a time and keep your perfect station intact and possibly with new songs. You have much more control with a single seed song. With a single seed song per station it's a lot easier to go through your thumbs up's and down's to tinker with the station. The "I'm tired of this track" also works across all stations.
The advantage of add variety to existing stations is that you can add an unlimited amount of seed songs(you can only have 100 stations). You get more variety and unpredictibility(although you can use the quick mix feature).
Using multiple seed songs seems to treat each seed song as a separate station. Thumbs up's don't really transfer between them. Sometimes you even have to re-thumb's a song up if it appears on a different seed. But thumb's down's do transfer amonst seeds so it makes it easier to ban artists.
If you use a single station you can also thumbs up and down by artist which makes it easy to see how often you give thumbs to particular artists.
How to pick Station Seeds:
Pick Your Favorite Songs of All Time(The more frequently you listen to Pandora Radio the more generous you have to be with the songs you pick with seed songs, the more you thumbs down the more often you have to add seed songs, if you like to hear lots of new songs then the more you'll have to click add variety)
Pick a Song Just Because You Like the Singer
Pick a Beautiful Song if you Don't Like How It's Sung(If you love "Your Song" but don't like Elton John then try to find a cover you like for example the one by Ellie Goulding)
Pick a Song Because You're Curious What It Sounds Like(Listen to the Song Elsewhere or Hope it Comes Up Organically)