Some people believe that fashion in a dream signifies new clothes or an upcoming new season. It could also mean that someone is making a statement with their clothing and wants to be noticed.
For example, if you are wearing your most expensive outfit to bed then it can mean you want to get some attention or if the scene of the dream is at a party, then it could signify your desire for social acceptance and admiration.
Sometimes, you are dreaming about fashion because you have an interest in Hollywood gossip or stories from runway shows so it might be that you just need some distraction from reality.
It can also symbolize vanity and pride, depending on what kind of clothes you are wearing or even your own sense of self-worth or lack thereof.