does not clash with the background color. Depending on your background colors, red, white and yellow often work well.
You can bold, italicize, or underline words and phrases for emphasis. Use italics and underline sparingly. If overdone, you’ll loose the affect and reduce the readability.
You can make your text stand out with special type effects such as drop shadows and outlines, but use these effects sparingly.
Use capitals only for short headings. Sentences or paragraphs in all capitals letters are hard to read. For longer headings, use upper/lower case.
Consider placing the author’s name and the web site URL as a watermark on the cover graphic to make it harder for people to steal your images.
Put your book title on the spine of large book and box images.
There are literally thousands of fonts to choose from. Build a small collection of fonts that work well for ebook cover design. This collection will probably include the standards like Impact, Arial Black, Arial Bold, Helvetica Black, Helvetica Bold, Times New Roman, Garamond and other fonts you like that are readable and practical in smaller sizes.
Like just about all rules, most font rules can be broken. The bottom line is, if your prospects can not read your book title, or if your ebook cover conveys a message that is not appropriate to your subject, then your choice of font can result in a loss of sales (or free downloads).