Similes are very simple.
Simile just means that one thing is similar to another.
It takes the formula:
[first thing] is like [second thing]
If the phrase has 'like' in it, then it's a simile.
The sun is like a golden yolk
My friend has a temper like thunder
My armpit hair is like an impenetrable jungle
Her smile is like a thousand summers
A simile can also use the word 'as' to draw comparison. This is the same as saying 'like':
The whisky was sharp as poison
Her hair was black as night
The stars were as bright as a blizzard
He was as funny as the plague
The very best similes tend to link two things that you wouldn't usually directly associate (the sun and an egg, a smile and summer) and finds a visual or emotional connection that makes sense on some level. For instance, when someone is shouting at you, it can shake you like an earthquake.
Examples that don't work so well:
Her laugh is like an ant running up a tree
My car drives like an orange
His eyes are as big as sponges
The moon glows like a frying pan
They're just too obscure to see a connection there. Maybe the moon glows like fire, but a frying pan doesn't really glow. An orange doesn't even move, so how can a car drive like one?
You also need to be careful not to directly relate something to what it actually is, such as:
The sun was like a ball of light in the sky
The milk was sour like something that had gone off
His poem was like words in verse
The mist was like a low-hanging cloud
This isn't really simile, it's just explaining what something really is.
The real pleasure in a simile is when it's creative but still makes sense.
Some of my favourites include:
The obsidian from the water pot was lying under the kettle like the lost eye of a bat. (Tail of the Blue Bird, Nii Parkes)
Dawn filled up the sky like milk poured into a glass bowl. (The Mountain Can Wait, Sarah Leipciger)
Souls cross ages like clouds cross skies. (Cloud Atlas, David Mitchell)
His guilt was thick in the air as winter mists. (Circe, Madeline Miller)
Her laugh was like a song that made you want to sing it. (Uprooted, Naomi Novik)
I kick him like thunder and he jump like lightning. (A Brief History of Seven Killings, Marlon James)
The rising sunlight spread like glittering marmalade across the toast of God. (Will Save the Galaxy for Food, Yahtzee Croshaw)
Her eyebrows shot up like the birth rate nine months after a prolonged power outage. (Will Destroy the Galaxy for Cash, Yahtzee Croshaw)
Of the Song of the Shadow, there remain only a few scraps of legend, carried like driftwood from isle to isle over the long years. (A Wizard of Earthsea, Ursula K. Le Guin)
Free association can be a good starting point with simile. When you look at a word, what else comes to mind?
Give it a go and see what you come up with:
The sun is like _____________________________________________________
The clouds are like__________________________________________________
The man was as angry as a___________________________________________
The water tasted sweet as____________________________________________
The woman smiled like_______________________________________________