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 the cat that got the cream (UK) / Like the cat that ate a canary (USA)
If someone looks like the cat that got the cream they look pleased with themselves, self-satisfied or smug (usually after having achieved their objective).
E.g. After his promotion he spent the rest of the day looking like the cat that got the cream.
Like something the cat dragged in.
If you compare a person to something the cat dragged in you are saying they look very untidy, unkempt, dirty or bedraggled.
E.g. After playing outside in the mud and rain the kids came home looking like something the cat had dragged in.
Have fun learning English!
Louise