Consider boosting the shopping experience with a thematic navigation section
As users may be searching for something that is seasonal or that they need for some occasion, or a specific use case - it makes a lot of sense to have such navigation!
Do not miss this navigation core guideline for starters
Your product categories should always be the first level of the main navigation, and categories and subcategories must be visually structured (always keep a View all link per category and subcategory). All other site links or pages should be visually separated (such as Contact, About, Stores, FAQ, etc). No matter the page, the user should always understand from the navigation - where they are currently, so make it visually clear (underline, make bold, use color, etc).
Help users to understand the importance of the navigation items by highlighting more important items in the design
Make the levels and importance of paths clear to users by tweaking the structure, size, or colors of the navigational items. You can use thumbnails or icons for key categories and show the subcategories without images, as an example.
Keep the navigation consistent and accessible though-out the site
Accessing the navigation extremely fast should be self-explanatory. Keep it visible and accessible, and consistent. As an exception, do not have the main navigation visible in the checkout flow.
Keep the support hours and contact details visible together with the Frequently Asked Questions page.
People may need to reach out or read the FAQ section, keep it highly accessible.
Consider showcasing highly popular filters, sales/deals as dedicated category pages, as well as the "New In" filter.
By understanding what are the key filters people use on your site, you should turn them into a category page and save users a great number of clicks and taps. Consider it as a user's shortcut to the desired products.
Keep my account and wishlist as part of the main navigation on desktop and mobile, and on mobile allow users to sign in and sign up from the mobile menu too.
Help people to access the core elements of your site from the header area, which is kind of the steering wheel of your website.
The bonus checklist
Try to include relevant and visual campaigns in your navigation
Present attractive visuals of your specials and campaigns inside the navigation menus. Example: imagine it is Autumn, and you click on the Accessories menu link on a fashion website. What you should see is a banner/visual with "Autumn accessories"
The “please avoid” checklist
Avoid showing sub-sub categories on the main menu, to avoid users overly narrowing their results
Be cautious while going too in-depth, most of the time it is good to lead the user just to the subcategory and allow them to filter out the products themselves.
Avoid opening up the dropdown menu while hovering on desktop devices
If you allow users to open menus on hover, it means you expect them to know everything by heart. That is not the case, and do not do it. Make the navigation open with a tap or click.
Avoid poor page speed
One two three four five six .... Bye-bye. Speed equals money in your pocket. Remember that, keep your Google page speed index above 90 on desktop and above 70 on mobile.
Avoid poor design, bad use of colors, and low contrast
It has been proven with research, that every 1 USD you invest in design and user experience improvements brings back 100 USD on average (https://tinyurl.com/wunderfront). Do not underestimate design, first impressions, and color psychology. Keep navigation and call to action of high contrast.
Avoid reinventing the wheel
Instead, use plugins, and ready-made software to cover these core guidelines.