A form can be difficult to use if it is long or complex, especially for people who have problems reading.
Although the flow of a form can make sense when viewed visually, it may be completely incomprehensible for people who use alternative devices (screen readers, Braille).
The form must be properly structured and optimised to support access technologies.
Adequate error prevention and good error messages are also important.
Before you begin creating your form, take time to plan and design it carefully. A form with good layout and that is easy to use will benefit all users.