In designing a Web user interface or UI design in general, you have to make sure that the user or the audience is able to perform what you want them to perform with ease and without confusion. In terms of navigation, it should be very obvious and very interactive in a way that it guides the user to flow through your website.
The UI is important on every device because it's the first layer of design that directly communicates with the user. If the buttons are confusing and abstract, then your target audience will not know how to navigate, and this will reduce the conversion rate of your site or your application. Check out these notes to help you out.
Try a grid.
A grid is an amazing way to structure your website. It gives a very broad and great perspective on all your website content at a glance. A grid can also be used in a very unique way by having graphic matches based on the grid layout you have set up.
Image source: http://zengrids.com/images/limitless-layouts.png
A grid is also bespoke and can be modified in whatsoever manner you feel comfortable with. Organizing your content this way will give your users a clean page to look at, and for devices like tablets and phones, you can also use gestures to control your grid more efficiently and precisely.
Use email sign-up forms.
Alright so this may come as a surprise, but having an email client embedded in your webpage will significantly increase your conversion rate and generate organic traffic. You can use Mailchimp or Constantcontact for example, and have your visitors sign up to your newsletter. It will allow you to legally send them promotional emails and have them contact you back as prospects.
In your design there are many places to include a sign-up email. Either you can have it in the footer or as a pop-up. A professional site will have it in the footer to avoid spamming users with a sign-up form, but for shopping-related sites, people do expect sign-up forms so that they can receive your offers and discounts.
Image source: http://blog.mailchimp.com/wp-content/uploads/2013/05/List_Final02.png
It is very important that you maintain consistency in your site throughout, from the landing page to the end root page. Consistency gives more credibility to the site, plus it looks more professional and shows that you are serious with whatever you are promoting. Having a site with design content from all over the net and a compilation of stock images is just very outdated and doesn't look professional.
Lastly, always keep the user in mind. Whatever's the easist and most convenient for them is usually the way to go.