Start with something you already reach for: a jacket, a pair of trousers or a shirt that feels comfortable. Keep that piece constant while changing one other element.
Change one proportion
Try a shorter outer layer with wider trousers, or a longer shirt with a more defined bottom half. There is no single correct balance; the aim is to notice what feels natural on you.
Use a simple color reference
Repeat one color or a similar tone across two pieces. This can make an unfamiliar combination feel connected without requiring everything to match.
Take a quick photograph if it helps you compare. Comfort and movement should have as much influence as the view in the mirror.