Giving an actionable design critique can be a daunting task, especially for the non designer. Here, I outline three steps allowing you to give a well rounded and actionable critique on design.
The first step is to describe the design. Who designed it and for whom? Are there requirements for the design that need to be met? Were there goals laid out by the client or the designer that were to be accomplished?
Asking these questions will put your view of the design in context. Aligning the goals of the design with context will allow you to remain unbiased when evaluating the work.
The next step is to observe the design. Look at things like color, form, texture and typography. Note the nuances of the design. Pay attention to patterns in the design, do they remain consistent or do they break? Get as detailed as possible in your viewing of the design. Try squinting, see if you can make out a visual hierarchy, essentially what items do you see first in the design? For example, do you notice the large bold header before smaller surrounding text? Lastly, take a step back and view the design as a sum of its parts.
The last step is to ask if what you observed and the intent of the design match. Are there visual inconsistencies with the goal and the actual design? Does every piece of the design make sense for the goal of the design?
Follow this guide to give your designer actionable feedback. Take it a step further; research design feedback, find an introductory book on design, take time to familiarize yourself with design vocabulary. Once you know the language, you can speak to your designer with greater effectiveness.