I would recommend 'A Dog's Tale'. It's not too complex and it has a really engaging story told from the point of view of a dog. It shows Twain's ability to create interesting characters even if they're not human. Another good one is 'The Story of the Bad Little Boy' as it has a simple plot but still has Twain's signature style of turning expectations upside down.
One of the well - known short stories from Twain is 'The Celebrated Jumping Frog of Calaveras County'. It's a humorous tale about a bet on a frog - jumping contest.
Some of his best short stories include 'The £1,000,000 Bank - Note'. It's an interesting exploration of how money can change people's perception of someone. 'Eve's Diary' is a charming and somewhat humorous take on the story of Adam and Eve. Also, 'The Story of the Bad Little Boy' is a different kind of moral tale, not like the usual ones, as it shows a bad boy who doesn't really get punished in the traditional sense, which makes it quite unique.
I'd recommend 'The King of the Golden River' by John Ruskin for beginners. It has a kind of fairy - tale like surreal quality with its magic river. Also, 'The Selfish Giant' by Oscar Wilde has a touch of the surreal when the giant's garden changes with the seasons in an almost magical way. 'Bluebeard' is another story that has a surreal and somewhat dark undertone, especially with the locked room full of secrets.
For beginners, 'The Double' by Fyodor Dostoevsky is a good start. It's a classic that really delves into the concept of the doppleganger in a very psychological way. You get to see how the main character's world is turned upside down when he meets his double. It's not too long either, so it's quite accessible.
I'd recommend 'All You Zombies -' by Robert A. Heinlein. It has a really cool concept that's easy to follow once you get into it. 'The Star' by Arthur C. Clarke is also a great beginner's story. It combines science and religion in an interesting way in a future - setting. 'Surface Tension' by James Blish can be a good start too. It presents a different kind of world and the challenges faced by its inhabitants, which is a common theme in futuristic short stories.
If you're a beginner, 'The Legend of Ghal Maraz' is a must - read. It's a short story that is full of action and at the same time, it tells the origin of a very important weapon in the Warhammer lore. 'The Skaven Invasion' is also good. It shows the sneaky and devious nature of the Skaven, one of the most feared races in Warhammer. And 'The Knight's Vow' is a story that can introduce you to the concept of honor and chivalry among the human knights in the Warhammer world.
I would recommend 'The Adventure of the Speckled Band'. It has a straightforward mystery that is both exciting and not too complex for those new to Sherlock stories. Another good one is 'Silver Blaze' as it has a simple yet interesting plot that can introduce new readers to Holmes' methods of deduction.
For beginners, 'Aesop's Fables' is a wonderful choice. It has simple yet profound stories with moral lessons. Each fable is short and easy to understand, like 'The Tortoise and the Hare' which teaches the value of perseverance. These fables have been passed down for generations and are a great introduction to the world of short stories.
Another great one for beginners is 'The Fog Horn'. It's a story about a lighthouse keeper and a sea monster that is attracted to the sound of the fog horn. It has an element of mystery and wonder, and Bradbury's writing style is easy to follow in this story.
For beginners, 'The Hole Man' is great. It has a clear plot and shows Niven's ability to tell a good story with a bit of mystery and some interesting character interactions.