There are many expressions commonly used in English with the comparison form ‘as … as’.
There is no magic rule to help you remember them. You just have to learn them. Sorry!
Take a look at the examples below.
As pretty as a picture.
If something or someone is as pretty as a picture it means it / they are very attractive, very beautiful or very pretty.
E.g. The lovely cottage dates from 1750 and is as pretty as a picture with its secluded location and extensive garden.
As straight as an arrow.
If someone is as straight as an arrow it means they are totally honest.
E.g. You can trust him with anything. He’s as straight at an arrow.
As drunk as a skunk.
If someone is as drunk as a skunk they are very, very drunk. They are extremely intoxicated.
E.g. She had only planned on staying for a couple of drinks but by the end of the evening she was as drunk as skunk!
Have fun learning English!
Louise