The idea behind contrast is to avoid elements that are merely similar. If the elements (type, colour, size, line, thickness, space and shape) are not the same, then make them very different. Contrast is often the most important visual attraction on the page. Contrast on the page draws our eye to it; our eyes like contrast. If you are putting two elements on the page that are not the same, such as two typefaces or two line widths or two colours, they cannot be similar. For contrast to be effective, make them very different.
Nothing should be placed on the page arbitrarily. Every element should have some consciously designed visual connection with another element on the page. This creates a clean, fresh look and intentional look. Unity is an important concept in design. To make all the elements on the page appear to be unified, interconnected and interrelated, there needs to be some visual tie between the separate elements. Even if they are far apart on the page, they can appear connected or related simply by their placement on the page.
Repeat visual elements of the design throughout the piece. You can repeat colour, shape, texture, spatial, relationships, line thickness size and type. This helps develop the organisation and strengthens unity visually.
Items relating to each other should be grouped close together. When several items are close proximity to each other, they become one visual unit, rather than several separate units. This helps organise the information and reduces visual clutter.