Highlight either required or optional fields
Whether it's because they are reluctant to share information online or just in a hurry (or both), many people give up on forms that ask too many questions. That's why your forms must clearly state which fields are required and which ones are optional. Sites often use one or more of these techniques to highlight fields:
An asterisk (or other icon) next to the field
The word "Required" or "Optional" next to the field
Required field titles in boldface
Try to minimize the number of required fields whenever possible. You'll still get the information you need but you'll also let customers decide whether it's worth the time to provide extra data. If you don't identify required fields, customers may become frustrated when told that an unmarked field is actually mandatory. They may even bail out of the process completely.
Turned Off http://www.victoriassecret.com
This "Create an Account" page at Victoria's Secret isn't as clear as it could be. Required fields, such as "Name" and "City," are not clearly indicated. And although some fields are tagged as optional (for instance, "Business Name" and "Evening Phone"), the site neglects to mention that the marketing questions at the end (for instance, "Do you currently receive Victoria's Secret Catalogue by mail?" and "Do you shop Victoria's Secret for yourself?") aren't actually required (you can skip them and still successfully create an account).
It would be better for the site to avoid the impression that these questions are mandatory when they're not. Otherwise, customers who don't want to share this sort of personal information may decide the process isn't worth the effort.
So how should you mark required fields? Use an asterisk or other clear icon to indicate which fields are must-haves.
Marked With * http://www.washingtonpost.com
The Washington Post uses a red asterisk to indicate the fields that must be completed. This means customers don't have to wonder, "Can I skip this field without causing problems?"