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.
(To be) like watching paint dry.
We use this phrase to describe an event or an activity that is very boring, dull, tedious or uninteresting. It doesn’t hold our attention.
E.g. I had heard that the new film was supposed to be really good but I didn’t like it at all. Nothing happened! It was just so boring. It was like watching paint dry.
(To be) like a bad dream.
If something is like a bad dream, it is so awful or unbelievable that it does not seem true or real. It is so unpleasant that you find it hard to believe.
E.g. The terrible events of yesterday still seem like a bad dream, but unfortunately they are true. I hope those affected can fully recover.
Have fun learning English!
Louise