Here are 5 key principles of good website usability:

• Availability and Accessibility. Let’s start with a basic, yet central aspect of usability: the availability and accessibility of your site. If people try to access your website and it doesn’t work — for whatever reason –your website becomes worthless.
• Clarity. If you distract or confuse your visitors, they will either need more time to find what they came for, or they might forget their initial goal all together.It is your job to help them reach these goals as quickly as possible. If you can manage to do that, your visitors will be pleased and you have laid the groundwork for a positive experience.
• Learnability. It should be your goal to design intuitive interfaces — interfaces that don’t require instructions, or even a long process of trial and error to figure them out. Key to intuitive design is to make use of what people already know, or create something new that is easy to learn.
• Credibility.It is important that people know you are a real company with real people. Offer a clear “About Us” page together with your contact details and if possible a physical address.
• Relevancy.It is not enough that your website is clear, your content must also be relevant. Again, it is essential that you know your users and why they visit your site.