Language 
A first condition for an efficient, consistent communication is that you always address the user in the same language. This may seem evident, but on multilingual sites this is very often not the case. Even single language sites in a language other than English sometimes make the mistake of providing feedback or error messages in English, because that's the language most programmers use as a default.

Tone 
Depending on your target audience, you will adopt a certain tone in the communication with your users. That tone comes through in different aspects of communication; in your writing style, but also in the way you address the user. In English there is only one personal pronoun for the third voice, "you", but in French, Dutch and German for example there are two, one formal and one informal. Take care to always be consistent; it is very unprofessional for a Dutch-language site to sometimes address its users with the formal "u" and sometimes with the informal "je".

Standardised dialogues 
If you offer a number of different forms on your site, make sure all the forms are structured in the exact same way, with identical terminology and order of the fields. Try to also word the instructions and feedback messages in exactly the same way. By always using the exact same turn of phrase, you create a sense of uniformity that not only makes it easier on your users, it also looks a lot more professional.

Identical buttons 
The rules that apply for the instructions and feedback of forms also go for the buttons: if the same button appears on several pages, always use the exact same words and spelling. If your site has several different forms for example, don't use one type of button at the end of one form and another button at the end of another form but always use the same simple 'Send' button.

Consistent layout 
The communication with users isn't limited to the texts on your web site, the layout of your site also communicates a message. The same rule that goes for verbal communication is also true for visual communication: be consistent. Especially on e-commerce sites, consistent visual communication is very important. Users find it very confusing when a site takes them to a page that looks completely different from the rest of the pages from that site and they often start wondering whether they're still on the same site. Users are very hesitant to trust their credit card data to a site that doesn't even succeed in making all of its pages look the same way, especially if it's the payment page that has a different look and feel.

Els Aerts & Karl Gilis