Ask only for what you need
Every extra field adds effort. Keep the first request focused on information that is necessary to respond or complete the task.
Group related fields and use examples where a format might be unclear.
Validate with a helpful explanation
Tell people what is wrong and how to fix it. Keep entered values when validation fails, and move focus to the first error when that makes recovery easier.
Use browser validation where it helps, but also validate and sanitize data on the server.
Confirm what happened
After submission, show a clear success or failure state near the form. Disable duplicate submission while the request is processing, and make retrying easy if it fails.
Test the full flow with a keyboard and a screen reader, not only the visual appearance.