Browser Compability
A website should look good and work as expected no only on all devices, but also (and probably more important) in all modern browsers.
Since the users are widely spread across Googles Chome, Firefox, Windows Internet Explorer, Safari, Opera and others, one very important part of the developing process are the so called cross browser tests. This means, I make sure that everything looks good and works on all popular modern browser versions.
This doesn't only mean to avoid errors and bugs, but also make use of features that might be offered by some browsers but aren't by others.
» Read more about cross browser development
» More about why I am not supporting IE6 ;)
Creating Useful Features
One thing that really strikes me when I see websites even of big companies: they put so many fancy features on their website, that the user is too distracted by unimportant stuff and information that he cannot find what he is actually looking for.
Reduce features to the ones that are actually useful for your clients and that support your sales.