Every field costs completions
This is the one rule that matters. Each additional field reduces the number of people who finish, and the effect is not linear — some fields cost far more than others.
Phone number, company size, budget and job title are the usual offenders on B2B forms. All are useful; none is worth what it costs at the first contact, because you can ask in the reply.
Decide what you actually need
For each field, ask: what would we do differently based on this answer, today? If the answer is nothing, or if the answer is “we would ask about it in the call anyway”, remove it.
The strongest enquiry form we deploy asks three things: who you are, how to reach you, and what the problem is. Everything else is a conversation, and the conversation converts better than the form field would have.
Validate as they type
- Confirm valid input immediately rather than waiting for submit
- Say what is wrong and how to fix it — “this needs a UK postcode, like M1 4WB”
- Never clear the form on an error
- Keep the error message next to the field, not in a banner at the top
- Accept formats people actually type: spaces in card numbers, phone numbers with country codes
Design for a phone in one hand
Most abandonment happens on mobile. Test the actual experience: does the keyboard cover the submit button, does the numeric keypad appear for numeric fields, can it be completed one-handed on a slow connection?
Autofill matters too — correct field names and autocomplete attributes let a browser fill half the form instantly, which is the single biggest completion improvement available.
Multi-step, when it helps
Long forms convert better split into steps with a progress indicator, because each screen looks achievable. The rule is that step one must be the easiest, so people start.
Save progress between steps. A form that loses everything when a phone call interrupts it is a form that will not be finished.
Never lose a submission
Write the submission to durable storage before doing anything else, then send the notification. Email delivery fails more often than people assume, and a form that quietly loses enquiries is worse than no form.
Log every submission with a timestamp, and give someone a way to see them independently of email. It costs almost nothing and it has saved several of our clients real revenue.