Usability is a key issue for sites offering services or selling something. Once you solve this problem, your visitors will feel comfortable and secure. Otherwise, their every move will be complicated by a number of obstacles resulting from your own faults.

You can be sure that after stumbling over one or several of such faults, very few users will stay at your site instead of going to another one, as they can choose from a couple hundred of other results found by Google. Keep it in mind: every time when something like that happens, you lose a potential client. You can avoid this by following some basic principles described below.

In some cases usability is not the top priority when planning the site. It can happen because some areas of the site may be restricted, or for safety reasons. Obviously, such cases will not be examined in this article.
   
Principle 1: be objective

Unfortunately, the overwhelming majority of present-day webmasters think subjectively, which means they are guided by personal perception and ideas about usability of certain tools and materials at the site. In truth, it’s always worth taking into consideration public opinion and simple logic.

The only correct way of solving the problem is testing. Unlike commonly (and wrongly) believed, this task is neither costly nor strictly professional, requiring a great deal of expertise and experience. You can read about this in more detail in Steve Krug’s book (the list of recommended books is provided at the end of the article).

Principle 2: correct navigation is a guarantee of success

The user should understand where he is. There are a number of ways you can help him.

Firstly, you shouldn’t neglect the use of links that change color depending on the status, even though they have lately become less current. Obviously, their use is not always appropriate, but if site design and concept allow for it, you might as well take advantage.
Secondly, similarly to street plates and house number plates, a website may have a linear «tree» of sections, for example «Main>Merchandise Catalogue>Samsung>without dust bag>SC9560», where all but for the last point being viewed should have hyperlinks.
Thirdly, it’s important to design an intuitive main navigation menu supplied with different visual «hints». The links must be easily recognizable and the user is not supposed to have a single reason to guess where he will end up by following them. Make the menu «obvious»!
Let’s take this nice site, for instance. Even though the design is very cute, the visitor using the F-shaped reading pattern to study the page might end up asking himself a question: «What is this site about?».
 
The reason is the description block shifted to the right. It should’ve been placed closer to the beginning of the document.
Here you can see the correct approach: introductory information is at the very beginning of the page!

Principle 3: define your content priorities

The content should be easy to read. Emphasize headings, subheadings, and other essential elements, as very often the page content is not read subsequently, but just scanned by the user for the object needed. Big documents have to be broken down into several pages. In case the reader would like to go back to some page it will save time required to find the material needed.
In most cases users that did not find the word combination, image or any other material they were looking for leave the site and get back to search. For this reason, it’s essential to carefully think through all the visible «key points». Proper design can also help with the content. Large images are especially effective in this case. You can see how it works at the humanized.com site, for example. 

Principle 4: design should be simple enough

The secret of successful design lies in its moderate (the word is in bold for a reason) simplicity. In spite of the blooming critique of the «web-2.0» style, some of its elements are still very efficient. Take for example large buttons, logos, entry fields. All that helps the user to use the site, instead of looking for the necessary function or object.
  
As for the «overloaded» design - this has never been welcomed by users. Ever!
 
Principle 5: keep to the existing standards of content design

Big text blocks without illustrations and with keywords in bold or italics are most likely to be ignored. The recommended «dosage» is the following: no more than 18 words (or 50-80 symbols) in one row, no more than three different fonts at the same time.

Additionally, you should come up with your own style and stick to it later on. Avoid complicated constructions, narrow terms and so on.

Emphasizing with color (not only text, but also the background) can help the user to better interpret the content.

Principle 6: make good use of empty space

Empty space is a great way to separate information. The use of this technique almost always has the edge over other designer solutions – and there are a number of reasons for that.

Principle 7: observe elementary standards

Let’s take, for example, the use of a properly selected site logo visible to the clients at the top of each page they view. This will allow the users to distinguish your site among others later on. It’s generally known that significant (in most cases prevailing) amount of traffic is supplied by visitors following the links found with the help of search engines, these visits often effectuated to internal pages. Firstly, a logo makes it possible for the user to remember whether he has been here before. Secondly, using the logo as a link to the main page is a widely accepted standard. Trust us: you don’t want to stand out for losing this opportunity.

Principle 8: functionality should be available

Don’t hide the functionality of a certain page or site in general. You should make active objects (text hyperlinks, images and so on) clear and easily recognizable. Moreover, the user has to know in advance where he is being led – for this purpose you can use descriptions and hints.

If there is a search field at your site, by no means should you overload it with all kinds of options, as this can discourage the visitor from using it. Such functions as unfolding lists and radio buttons will look much better on a separate page, for the integrated form to be concise.

A good example of «correct search» is an online retailer Amazon.com. The search system installed identifies the pertinence of any data entered to the necessary category, say, author, article or product name. 

Principle 9: don’t try to save on content

Don’t think that creating a user friendly website has nothing to do with its content. The truth is - if the quality of such a site is not very high, or it is poorly built, the users are most likely to face certain difficulties when using it. 

They all appreciate quality and reliability. Make sure you offer quality content, and advertisement will never become an obstacle to using the site and feeling comfortable. It’s a fact: content is a lot more important than the design supporting it.

Principle 10: do not interfere with the browser

All users, with no exceptions, are willing to feel in control of the resource they are viewing. The most common mistake is irrational use of pop-up windows and opening links in new tabs.

Principle 11: test, test, and… test again

One thing you need to understand is that there is no single definite solution of the usability problem that would be equally suitable for all the variety website topics and concepts.
Don’t get stuck in one place – explore and experiment, and you will surely get lucky!

Summary

Usability is a precise design structure, its clarity and simplicity; it also implies lack of doubt or questions.
This subject is fully and properly covered in the following books: The Practice of Simplicity (Jakob Nielsen, 2000) (contains detailed and illustrated analysis of the usability discipline with examples), Prioritizing Web Usability (Jakob Nielsen, Hoa Loranger,  2006) (the edition offers a big number of ready-made solutions and examples of the correct approach to the issue of creating websites), Don't Make Me Think!: A Common Sense Approach to Web Usability (Steve Krug, 2005) (if compared to Jakob Nielsen’s work this material is more simple to understand).

(contains detailed and illustrated analysis of the usability discipline with examples), Prioritizing Web Usability (Jakob Nielsen, Hoa Loranger,  2006) (the edition offers a big number of ready-made solutions and examples of the correct approach to the issue of creating websites), Don't Make Me Think!: A Common Sense Approach to Web Usability (Steve Krug, 2005) (if compared to Jakob Nielsen’s work this material is more simple to understand).