Ensure each input field is clearly labelled so the reader knows what data is expected. Figure 6 shows one example of such grouping. If any fields are mandatory, say so rather than letting the reader discover this when they submit the form. Beware making the form too big.
Huge forms can be unwieldy to scroll through and difficult to understand.
The reader may give up part way through and you will get none of the fields that they have filled in unless they use the submit button. It would be better to use a series of linked forms with hidden fields than one huge form.