There are three navigational structures that are used, in combination or individually, on websites. Each of these navigational units can help contribute to improved rankings; however, before they can contribute in a positive way, we need first make sure they are not creating problems and hindering potential rankings.
Generally, the main navigation appears below the masthead as a row of links (and often drop-downs) which allow users to navigate through the website. Since the placement of the main navigation usually results in a lot of links before any of the website content is displayed, it is important to make sure that even if the keyword-specific optimization is not taken into account during navigation, it should at least not be a drag on rankings. For example, if you have a large list of categories of products (services, topics, etc), do not try to stuff every single category into your main menu. This will take away the ability of every page of your website reaching its whole potential in terms of ranking because of the main menu being top-heavy.
The footer navigation is traditionally for non-important links that do not need to be
The secondary navigation, which can usually be found on the side of certain pages, can help relieve the load off of the main navigation, as you wouldn’t have to have multiple nested dropdowns which contribute towards making the main menu top-heavy. Instead of having less important or sub-sections on your site that have their own dedicated main navigation links, it is helpful to have those secondary links appear on the side of your pages where appropriate. For example, if you are selling clothes which are categorized by type of fabric, color, and size, instead of having a dropdown menu in your main navigation that lists the various factors, it would be better to have one link in your navigation which points to the widgets page. This would give your visitors (and search engines) side navigation options so that they are able to dig deeper into your subcategories based on fabric, color, and size.
Every category that your company may have, may also have a list of subcategories under each of them. Obviously, you cannot add each of these in the main menu. However, the example given above should give you a gist of how you can utilize your site navigation to ease the burden off of your main navigation.