When designing a website to be viewed on a computer, it is important to take into account the different browsers that your visitors might be using. Different browsers interpret the tags in different ways, however by properly declaring your document using the DOCTYPE tag, you are more likely to get the results you are expecting.
When designing for tablets, one must remember that tablets are navigated by touch and generally have smaller screen sizes. The links must be separated, or large enough, so that when a link is touched, only the desired page opens. It can be very frustrating for a visitor to your site to have difficulties getting the right link to open because they are positioned so close together. The screen sizes of tablets are also an area to consider. Generally they are smaller than laptop or monitor screens, therefore you should consider the layout size of your content. It is difficult and unnatural to scroll sideways on a tablet so you want to make sure that everything fits within the width of the tablet screen.
Making your website compatible with smart phone screens can be difficult. Some website designers recommend creating a separate site designed just for mobile devices because designing a site that is compatible for the phone, which would mean the longer screen width, larger links, and limited information on the page.