A racy sports car will be turned back more often than a utilitarian four wheel drive truck. Ensure that your entire message is well presented in the text of your pages. Use images to enhance the look of your pages, but avoid images that are critical to your message. A good test is to turn off image display on your browser and look at your pages. Use html extensions sparingly.
Less extensions means less potential for problems.
Most viewers will ignore commands they don't support, but what effect will this have on the format of your pages. It can turn a beautifully formatted page into an ugly block of scrambled text. Test your pages with various viewers. Install a couple of different versions of both Netscape and Mosaic on your machine and try each one. Take every opportunity you can to use other machines to view your site.