= Beginner
= Average
= Advanced
Some definitions (just to be acurate)
Font: The graphical characteristics of the characters.
Font size: for a given form of the characters, it represents the height, width and weight of its graphical representation.
For instance: A A A A A A
It is represented by numbers : -1, +0, +1, +2, ...
Font face: the form of these characters, straight, curve, italic, bold.
Font color: do I need to explain that?
Image: I guess you know what it is. You have seen it over and over on the web. The important point is that unlike common text you cannot put it directly in your HTML file. You will have to refer to it with an adress, that your HTML editor will ask you to give when you want to put an image. This adress looks like ./Image.gif, or ./Image.jpg, or even http://www.server.ext/subdir/image.gif, if you choose to use images that are not in your personal directory. These images are coded (in binary format) using three main coding conventions: the png, gif (now deprecated) and jpeg formats.
What can you use and where?
An obvious rule about font size and color is that it must remain readable. So don't use font sizes too small, nor colors too close from the background, unless you REALLY don't want it to be read... You might use clear characters against a dark background, or the opposite, but don't count too much on the difference between colors of the same light intensity, even red/blue, or green/yellow.: with old screen managers, it can become unreadable. It is advisable not to use font sizes under -1, but keep large font sizes for titles and words you want to highlight, otherwise only a few lines would appear in a browser's window... and needing to scroll ceaselessly is a sure way to make readers go away.
You can use the same color range for the text and for the background. On most browser you only get 216 colors, so subtle differences won't appear. (Remark for those who don't use a WYSIWYG editor, but actualy type HTML code: even if you code RGB colors on 3 bytes in HTML programs, the browsers only show a very limitated color range.)
Font face does not generally cause problems, and its use depends largely on what will be YOUR style.
About images...
A page constitued of plain text only is quite boring, but having to wait for hours for images to be loaded is still more boring.
So... use images, but efficiently and not too much! It is once again a question of balance. In fact you have three images formats (i.e. encodings) that you can use on the web: png, gif and jpeg. The first is a very efficent coding for low colors and transparent images (i.e. drawings). The second enables you to make animated images quite similar to video, to have transparency, but has only average quality, and leads to big files. The later makes quite smaller files, and it's quality is generally only limited by your screen properties. Generally you will use gif files for little images with graphic effects, and jpeg for hight quality, raw images such as photographs.
As for images files sizes, the maximum size to obtain a quasi-immediate loading is about 100kb. Above this size, readers will have to wait seconds, even minutes, to get the whole image. This must be kept for cases in which the image is really the important element, as for photographs...