Simple Mistakes Webmasters Make on Their Sites
Not matching case on URLs - Some operating systems require the case (upper or lower) of file names, directories and file types to match exactly. Thus, "Email" as a file name is not the same as "email". This is primarily true of Linux and Unix based machines, and the Apache web server follows this convention with URLs. Thus, it is important to remember that case must match.
People from the Unix and Linux world don't have a problem with this, as that's what they are already used to. However, those from the Windows platform (as well as OpenVMS) will often get tripped up because on those systems the case of any part of a file specification is not relevant.
I've found it's usually wise to make all file names, folders and file types lower case. This eliminates the problem.
Messing up the TITLE - The <TITLE> tag is important to an HTML page. It is displayed in the upper left portion of the browser to show the user the general topic of the page. In addition, many search engines use the title as the name of the page.
Many webmasters simply forget to include the TITLE tag at all, or leave it to the default of their editor. This is typically some variant of "new page", which definitely makes the page look less professional.
A huge sign of an amateur is a TITLE which is filled with keywords which do not make sense to a human being. People who are attempting to "fool the search engines" make titles which are just strings of words. Since these words mean nothing to the surfers who use search engines, it actually results in less clicks than would the same title worded in a way that makes sense to normal people.
Improper use of meta tags - META tags are used to relay information about a web site or page to outside entities. These include search engines, directories and robots (spiders) of various types. The information passed might include copyright data, keywords (to tell search engines what your site is about), a description of the site and many other things.
Some webmasters just include dozens of meta tags without really understanding why. The proper thing to do is understand what you need to communicate about your web site, then use the meta tags which are appropriate for that purpose.
Forgetting closing tags - Most HTML tags (and all XHTML tags) require an opening tag and a closing tag. Thus, a <TABLE> needs a </TABLE> and a <B> needs a </B>.
It's quite common for a webmaster to forget to include these closing tags. This can result in errors when a page is displayed in a browser.
Forgetting the </HTML> tag - Some browsers assume the end of the document is the same as the </HTML> and thus do not require that tag. It's best to include it always, however, as occasionally a browser will not render (display) the page properly without it.
Including header elements outside of the <HEAD> tags - This causes the elements to be ignored in some browsers (especially the newer ones).
Including body elements outside of the <BODY> tags - The elements are ignored in some browsers and displayed in others.
Referencing graphics and links using local file specifications - This makes a page which appears to work with it is tested on the webmasters local machine but fails when it is uploaded.
Forgetting that some people browse with graphics off - This is most glaring when a dark background is used with white text. If the background color is left to white, then if a person turns off graphics the text will be invisible.
Not including ALT tags on images and tables - This allows people with graphics turned off to understand what the graphics were for, and allows people with screen readers to be able to "see" your graphics and tables.