I just think about what I feel like the character would wear, and what types of outfits fit the situation the character is in.
For example, with Jayden in FTD, I searched for outfits that were casual, simple, and not girly at all. Jayden is definitely a tomboy, so I wanted her clothing to reflect that.
As another example, I have Kai in Blue Royalty, his style tends to be closer to a business casual as his standard instead of a casual. He’s used to an upper class elite lifestyle, and dealing with business an adult would even as a teen. He dresses professionally, ready for the life in the real world beyond the safety net of high school. He’s had to be like an adult before he even was one, which is reflected even in his clothing choices.
Though, I do find it unavoidable to not have some of my own influence onto my characters’ style. Though something may technically be something the character would wear, I find myself looking at it through my own view for whether it looks good. I tend to not have my characters wear more revealing outfits, because I can’t avoid thinking about my personal fashion sense, and how I personally am more uncomfortable by the thought of wearing revealing clothing.