A parti diagram should work like a manga: you can follow the story from the pictures without reading the words. Most student diagrams are drawings with labels. The real diagram is the visual layer in between.
Three steps, and the one everyone skips
Step 1. Make the drawing. The plan, the section, the axonometric: the base drawing of the project.
Step 3. Add the annotation. The words, the labels, the arrows with notes.
Step 2 is the real diagram. It's the visual layer you add on top of the drawing so the idea reads without the annotation. This is the step most students skip. They go straight from drawing to labels, so what they produce is an annotated drawing, not a diagram.
The test
Cover the words. Can someone still read the idea? If they can't, the diagram isn't doing its job yet. The annotation should confirm what the reader has already understood from the picture, not explain it for the first time.
Why it matters
In a crit you have minutes, and in a portfolio you have seconds. A diagram that reads like a manga gets your idea across before anyone reads a word. It also shows you understand your own project, because you can't draw an idea clearly if it isn't clear to you.
Next step: Bring a diagram you're working on to Mini Studio or Student Coaching, or book a free introduction.