There are many expressions commonly used in English to express similarity.
There is no magic rule to help you remember them. You just have to learn them. Sorry!
Take a look at the examples below.
Like a flash.
This is used to describe something that happens very quickly and / or suddenly.
E.g. As soon as I saw that spider in the room, I took off like a flash. I have a terrible phobia of spiders.
To go out like a light.
If someone goes out like a light it means they fall asleep very quickly or suddenly.
E.g. He was incredibly tired. He went out like a light as soon as his head hit the pillow.
Have fun learning English!
Louise