Watch Your Mouth!
Internet users are very autonomous and self-directed people. With this in mind, you will have to echo those character traits and use the right tone of voice to fit with them. You should also be very careful and really watch your mouth while talking with them, since they are just one click away to your competitors.
There is no correct tone of voice and approach towards interacting with website visitors. There are millions of them, and each of them is right for a certain type of website and business. What you can have in mind in all the cases is:
To master the right tone, try to think about what your potential customer really likes, what is he interested in and what can catch his attention;
Always be clear and direct while talking with your website visitors (your clients have enormous choice);
Be fast with providing response. It is better to give partial information immediately than the whole information and be late. Remember: Internet is all about immediacy and people are sick of WWWait - language;
Filter everything to its core, but be sure to keep the tone that fits with your corporate identity;
Throw away the dictatorial tone and use more pleasurable and persuasive voice;
Try to avoid incomprehensible and offensive words;
Write active sentences and engage visitors - do not use passive sentences. E.g. "You will be informed upon this issue" can be "We will inform you about the prices"
Strive not to use superlatives and claim that your products are incredible or astonishing. People have had enough of the everyday sales hype;
In any case: try not to be very persistent and try to oversell - they will surely notice it and they hate talking to sales people.
Give your website visitors their space and they will be grateful. Dante Alighieri once wrote: "Liberty is the prevention of control by others".