There are many ways, but this is my favorite way, through the eyes of an evil alternate universe version of my OC, Amber Faye.
First I go to Cloudsdale and get a job at Rainbow Dash's favorite resturaunt. I make friends with her, you know, talking while she waits for her food. Then I "lose"(quit and say I got fired) my job, and convince RD to let me move in with her. Being an Alicorn(don't ask, she's NOT a princess), I "accidentally" use a gender swap spell on myself, and make Rainbow fall in love with me. Then, I steal her element, and buy a house in Ponyville. Rinse and repeat, with slightly different curcumstances, staying a stallion all the time, never going back to a mare, untill I get to Twilight. I go to the library, looking for history book reccomendations, and while she is distracted, get her element. I then move to Canterlot, and join the royal guard, moving up the ranks untill I am Luna's personal guard. I use my stallion charm on her, and ask her to be my date to the Gala. I meet Celestia, then ask to see both of the princesses outside in the castle gardens after the Gala. I meet them there, and knock out Celestia with my dark magic, doing the same to Luna. I lock them in a chamber, where they can magiclay see everything that happens to their friends. I place special cones on their horns so they can't use magic, and clips on their wings so that flight is impossilble. I then bring Princess Twilight up to Canterlot, and put her in the same cell, at the other side. I then torture Spike and the Mane Six infront of eachother and Tia and Luna. I then Kidnap Cadance and Shining Armor, and use dark magic to bring Sombra back, and let him have the crystal Empire.
I'm evil, I know.