Form optimisation is increasing the share of people who complete and submit a form. The basic rule is to ask only for what you need for the next step – you will find out the rest in conversation. Every extra field, especially an optional one that looks compulsory, reduces the number of submissions. It helps to have a logical order of fields, clear labels above the fields instead of placeholder text inside them that disappears on click, the correct keyboard type on mobile, autofill, and immediate validation with the error explained right at the field. Word error messages specifically, not generically. After submission, clearly confirm what happens next and by when. For longer forms, split them into steps and show progress, or ask for details gradually, only once interest has been shown.
See also: Friction in the conversion process, Micro-conversion, Response speed to inquiries.
