Start, as in all such things, by learning to walk. In general, don't use more than two fonts in any page, and don't go overboard with colours. Strongly coloured backgrounds can make text hard to read; there are plenty of sites out there where the text is actually invisible in some browsers. Never put up a page that has only been tested in IE, which tends to "gloss over" mistakes in coding that other browsers will interpret literally, and bear in mind that different browsers will display various things in slightly different ways.

WYSIWYG website builders like Dreamweaver are useful, but can tempt the beginner into over-reaching themself; and will often insert URLs for images, for example, that point to a specific location on your hard drive rather than a relative link; this can result in a website full of empty boxes instead of pictures. The designer may remain blissfully unaware of this until told, because they can see all those pictures while nobody else can. Try to acquire at least a basic understanding of html so that you have some idea what you are doing.

Dreamweaver will not make a person a designer any more than a ten-minute bodhran tutorial will make a musician. There are a great many websites out there which are the design equivalent, come to that. Simple is always better than garish and ghastly. Avoid javascript and all "effects" to begin with. Remember that the web is not DTP; you can never be sure that people will see your work exactly as you hoped, and that if you define specific fonts, many people may not have them installed and will see something else entirely.

A good way of learning is to find a page that looks nice to you. Save it to your machine and look at the underlying code. Work out which bits do what. Pick up an html manual in a remainder bookshop so that you can look things up. Experiment with simple stuff first.

Basically, the advice that one gives to a beginner in any skill. Learn by imitation and copying to start with. Avoid most WYSIWYG programs (especially anything made by Microsoft, which will insert crap and unnecessary code all over the place). Don't export as html from a word-processing or DTP program. Try a text editor which will highlight code in a different colour so that you can see more easily what you are doing. Arachnophilia is useful (and free), and the earlier version, which I think is still available, has an integral browser for quick checking.

With due respect, the people you work for are rather ill-informed if they imagine that it is an unskilled job that anybody can do effectively without at least some understanding of what is involved. I daresay they would be quite shocked if they were replaced by the office cleaner on the grounds that "anybody can do that".