Realistically, you should pick a broad enough range of viewing criteria to accomodate viewing by both Netscape and Internet Explorer users at a screen resolution of not greater than 800x600. The quality of your pages speaks directly to the amount of attention you pay in maintaining them. It is not enough to work on a web page, upload it, and forget about it. With the availability of spell checkers, your site should exhibit good grammar. Java can be a tricky topic.
Applets are as susceptible to bad file path names as graphics and links.
Some applets and scripts aren't compatible with older browsers and may in fact, lock them up. When your page loads up, the first thing a visitor sees should not be someone's advertisement or icon. Animation can be good when used in moderation. When I review a web site, my screen should not appear to be crawling with all kinds of moving gizmos, furry critters, and shooting stars. Frames can enhance a site or they can complicate it.