This holds true for almost everything. Avoid long, unbroken text-only pages. These can be hard on the eyes, as well as the attention span. If you must include this type of information, try separating different topics using hard rules or images. Images can be overdone as well.
Large images are bandwidth hogs and often frustrate modem users due to long download times.
Remember that time is money. Where possible, warn users about large images contained in your page and include file sizes. Whether you are just learning HTML or are an experienced designer, remember that there are limits to your design skill. If you set out to build a page with features you don't really understand, you could wind up frustrated. That does not mean you shouldn't try and learn more complex HTML design skills, it simply means learn to use what skills you have to their full potential.