Every field costs you submissions.
THE PRINCIPLE
Ask for the minimum you need to respond. Everything else can wait.
WHAT TO ASK FOR
Name, contact method, and what they want. Usually three fields.
Add a phone field if you genuinely need it, and mark it optional unless it is essential.
WHAT NOT TO ASK
Company name, unless relevant Address, unless you need it to reply How they heard about you, which you can ask later Anything you will not act on
Each field loses a proportion of people.
LABELS
Above the field, always visible. Placeholder text that disappears when typing is a usability problem.
ERRORS
Say which field and what is wrong, next to the field. Do not clear what they typed.
THE BUTTON
Say what happens: "Send enquiry", not "Submit".
AFTER SUBMISSION
Show a confirmation on screen and send one by email. A form that appears to do nothing gets submitted repeatedly.
ON MOBILE
Use appropriate keyboard types: a number pad for phone numbers, an email keyboard for addresses.
TEST IT
Monthly. Forms break silently and you lose enquiries you never know about.