Princess Twilight Sparkle is one of the most eligible bachelorettes in Equestria. She's got a royal title, her own castle, and has never been on a date.
Rarity has been on quite a few dates, and they've largely gone poorly. This makes her the most qualified pony in Equestria to teach Twilight how to avoid embarrassing herself and win the stallion of her dreams.
There's no way anything could go wrong.
Thanks to AmpDragoness again for the lovely cover art!