Prefill the text fields, combo boxes, and other controls with
reasonable default values. You could do this when you show the
page to the user for the first time, or you could use the
information the user supplies early in the application to
dynamically set later values. (For instance, if someone
supplies a United States ZIP code, you can infer the state,
country, and sometimes the city or town from just that number.)
Don't choose a default value just because you think you shouldn't
leave any blank controls. Do so only when you're reasonably sure
that most users, most of the time, won't change it -- otherwise,
you will create extra work for everybody. Know your users!
Occasional-use interfaces like software installers deserve a
special note. You should ask users for some technical information,
like the location of the install, in case they want to customize
it. But 90 percent of users probably won't. And they won't care
where you install it, either -- it's just not important to them.
So it's perfectly reasonable to supply a default location.
Jeff Johnson discusses this issue at length in Web Bloopers:
60 Common Web Design Mistakes and How To Avoid Them (Morgan
Kaufman). He provides some hilarious examples of poor default