One by one, Twilight and her friends must come to terms with the consequences of being the Elements of Harmony.

These stories take place in the intervening time between Season One and Season Two,
with the exception of Ditzy Doo: Muffins, which takes place early in Season One.

The series continues in the sequel, Secrets and Lies.

Pony Psychology has a TV Tropes Page.

Twilight and her five friends are transported during a botched spell, across dimensions to... Ponyville, Equestria? But not the same one that they knew. Sitting on a bench is Harpsy and Babar. The Doctoress avoids apples from an aspiring Applebuck. And in a library across town, six stallions join their forces as they try to decipher the appearance of filly look-alikes of themselves around Ponyville!

Twilight Sparkle is a gifted student and scholar. When she attempts to harness her creative side by writing a science-themed sensual romance novel, however, things rapidly get out of hoof. Can her friends stage an intervention before she humiliates herself (and them) at a prestigious literature recital?

No. No, they cannot.

A day in the life, and a glimpse into the mind, of Ponyville's favorite mail carrier and single mom. But if she had the choice of any one day for everyone to read about, it probably wouldn't be this one...

Luna has had enough of Celestia's games, and has found the perfect means of revenge. Using a long-forbidden spell, she transforms her sister into little more than a small filly, all so she could pull the greatest prank ever. Unfortunately, she soon learns that before you fool around with dangerous magic, you really need to read the fine print...

A sequel can be found here.

Octavia is a high-class pony. Fine alcohol is her wont, and uncouthness her intense chagrin. Such is her surprise to find herself lumbered with an insufferable oaf of a DJ pony. However, sometimes these situations work themselves into a satisfactory ultimatum all the same.

Humans.

Truth or myth? Ancient lost civilization or just an old pony's tale?

No pony has ever seen one, and most haven't even heard of them. But Lyra knows that these wonderful creatures are more than just old legends, and she's going to find out... and possibly drive her roommate insane in the process.

Twilight is invited to Canterlot to compete with some of the greatest magicians in the world for the Moonstone Cup, a prestigious award for the most powerful and skillful magicians, unicorn and otherwise. Can she win? What sort of competition will she face?

Awesome cover image was taken from NoOneBahtim

When your life is as dull a gray as the world that surrounds you, the mundanities can make it all seem meaningless. Sometimes all we need is a little color -- or six -- to reintroduce us to what truly makes life worth living.

*6-16-2017 Edit, added Rainbow Dash tag because it triggered knighty.*

Rainbow Dash struggles to figure out why Pinkie Pie keeps acting weird, and seems so happy about spending Hearts and Hooves with hanging out with her, while also puzzling over the fact that Cloud Kicker and Blossomforth seem to be going out of their way to help the two of them enjoy the day.

Cloud Kicker and Blossomforth need to have their own tags, because they're awesome characters who deserve to have more stories written about them.

Has a semi-sequel-follow-up-side-story:"The Life and Times of a Winning Pony."