Some common mistakes to avoid include using a grid that is too rigid or inflexible, neglecting to balance white space and negative space within the design, and relying too heavily on the grid without considering other design elements such as typography and color. One way to keep a grid layout visually interesting is to incorporate variations in the size, shape, and placement of design elements within the grid. You can also experiment with different color palettes, typography, and graphic styles to add visual interest and texture to the design.