Keep a test site, and test well before you publish. Use the Xitami errors.log file to detect and fix link errors. To Avoid Like The Plague Blinking text. Lots of images, unless you are building an intranet site. Images can be very useful, but cost a lot in terms of preparation, maintenance, disk space, and network transport.
All programming is expensive, and executable content is particularly costly.
Like images, executable content is most often used for flash, not to solve specific problems. JavaScript, in small quantities, is probably the safest route to go for small adornments, since most browsers can handle it these days. CGI, unless you really need it and are aware of the costs and benefits involved. Good CGIs can provide a very useful level of interactivity, but you must know what you are doing. Cookies, unless you really know what you're doing.