Personality:

Despite being royalty, she often encourages her subjects to relax with jokes and gentle questions. She also shows great patience with any inappropriate behavior towards her, as seen when Pinkie Pie snatches a cupcake from her at a party in A Bird in the Hoof.

Celestia's mischief with tea cup refills.

Princess Celestia displays a fun-loving side when she chuckles at the bottle of disappearing ink sent to her by Twilight in Griffon the Brush Off. In A Bird in the Hoof, while sipping from a constantly refilled cup of tea, she pretends to sip from her already full cup, causing Mr. and Mrs. Cake to overfill it. She watches with a smile on her face when Pinkie Pie devours one of her cupcakes, while Mrs. Cake gasps and drags Pinkie away. Celestia tells Twilight and her friends in The Best Night Ever, after they ruin the Grand Galloping Gala, that she always found the Gala awful and she was hoping they would liven it up. In Make New Friends but Keep Discord, Celestia invites Discord to the Gala for this same reason, and by the end of the episode, she declares it to be "the most fun Gala in years."

While kindhearted and slow to anger, Celestia's patience does have its limits. When faced against the threat of Discord's return in The Return of Harmony Part 1, Celestia wastes no time in demanding that Discord return the stolen Elements of Harmony. Also, in Lesson Zero, when Spike makes her aware that Twilight inadvertently unleashed mass chaos onto Ponyville in her obsessive attempts to find a friendship report to send to the Princess, Celestia personally intervenes to undo Twilight's out-of-control spell. She sternly orders her student to a private meeting to discuss her actions but remains understanding, and at the insistence of Twilight's friends she agrees not to punish Twilight, instead asking them all to send her friendship reports only when the lessons make themselves apparent to them. In A Canterlot Wedding - Part 1, after Twilight accuses imposter Cadance of being evil with no evidence to back her claims, Princess Celestia, along with the others, makes clear her deep disappointment in her student and walks out on Twilight after Shining Armor and the other ponies. But in A Canterlot Wedding - Part 2, while displaying righteous rage to the newly exposed Queen Chrysalis, she eventually commends Twilight for her instincts that told her the imposter Cadance was evil.

So try to sound like her in the show.