"Form Design Best Practices"
It's vital to keep your form design simple. Its been proven that conversion can be increased when fewer fields are requested by a web page. Include only the most crucial information in the forms. Arrange the form fields from easiest to hardest. Leaving the hardest question last increases the probability that they will complete all the required fields. Align the field labels to the left, this makes it easier to read and complete.
"Designing Efficient Web Forms"
Avoid using "optional" fields. Users will typically opt to not fill in this field. These "optional" fields might even stop someone from completeing a form. Clearly written labels are imperative to an easy user interface. Keeping the labels simple and straight forward. Use sentance case opposed to title case. This makes the labels faster and easier to read.