The placement of every pixel must be considered. No detail must be left uncritiqued. No typo can be left unfixed. If something is off-center by the slightest degree, it can quickly become a visual abomination.
Take a first glance at the design. Then take a few steps back and look again.
Objective: That is the objective of the design?
Action: Will the viewer know what action to take in each area of the design? Call, click, read or visit?
Brand match: Does the design match the client’s brand?
Composition: What would improve the overall composition?
Client examples: Does the design meet or exceed the quality level of example designs the client has mentioned?
Inspiration examples: Does the design meet or exceed the quality level of example designs from your research?
Dimensions: Are the dimensions appropriate for the project?
Begin thinking about the main qualities of the project.
Eye flow: How does the eye flow through the design? Is the eye resting on the right elements in the right order?
Weight: Does the visual weight of the design elements work? Is there anything too heavy or too light?
Colors: Is the color palette working? Are there colors that seem to not fit the brand or design?
Typography: Are font choices appropriate for the design? Are there too many being used or too few?
Photos: Do photos and images match and support the overall design and messaging?
Messaging: Is the core messaging clear? Is there a headline or other text that needs to convey a certain message? Will people easily see what you want them to see?
Examine every pixel of the design in close-up detail.
Typos: Look at every single word.
Grid: Are design elements structured on the grid properly? Is there anything that could break the plane on the grid to add more interest to the design?
Alignment: Is there anything off-center or out of alignment?
Photo treatment: Have photos been treated properly? Are photos facing the proper direction? Are photos cropped effectively?
Typography: Is font usage consistent in the design? Is the text spaced properly?
Tangents: Are there any weird design tangents? The unintended visual tension between objects?
Great designers have a vision of both the big picture aspects and small details of the design.