Ask HN: How does one simplify UI design of a complex web form?

I am working on a project that requires a web form with about 40 fields of various types e.g. calendar, dropdown list, radio buttons, text fields, numerical fields, file dialog etc. Unfortunately I am not able to share the exact details of the actual form due to confidentiality. Hence I am seeking general advice on designing complex web forms.

I am looking for some inputs on how to start thinking on managing the complexity of UI design with lots of data entry fields. As I am not a UI designer I am bit overwhelmed by the size of the web form. What approach would a UI designer take when starting the design process of a complex form from both aesthetics and usability point of view?

I was thinking of grouping related fields together and revealing each group in an accordion style of design so that the user is not overwhelmed when entering the data. Is this a sound idea in general or are there better way to present complex web forms?