Start with one shape
Choose the part of the outfit you want to lead: a fuller trouser, an open shirt, a shorter layer. Give it enough space in the rest of the outfit to read clearly.
Look at the meeting points
The shirt hem, the top of the trouser and the place where the leg meets the shoe change the overall impression. Try small adjustments before deciding a whole piece is wrong.
Change one thing at a time
Roll a sleeve, loosen a tuck or change the base layer. Comparing a small change makes it easier to see which proportion feels like yours.