The following practices will increase the probability of a successful install.
Use the "www." in your URL. If your site can be accessed as both http://foo.com and http://www.foo.com, use the latter syntax when entering your URL. This helps prevent problems during path auto-detection.
If your install fails, try at least once with all of the optional fields blank. Many failed installs occur simply because a value was hard-coded. The installer auto-detection algorithms do not execute when a value is hard-coded.
Make your Website and FTP Path values agree. If you enter "public_html/cgi-bin/foo" for your FTP Path, then make sure your website value is "http://foo.com/cgi-bin/foo/".
Use trailing slashes. Enter your website as http://foo.com/cgi-bin/ rather than http://foo.com/cgi-bin.
"Best practices" http://www.xav.com/scripts/installer/3004.html