This is an interesting question as it depends on the developer! You may be familiar with what you should have for your web developer or a house developer, and the intent is the same with all people who will be developing something for you. What best explains what you need, when you need it, and how you’d like it done is what you bring to your developer.
For most firms there is an application process of some kind, a questionnaire, form, interview, etc. that asks the questions to best get that information from you to the developer. In addition to answering such questions, additional information should always be provided. Here’s a short list of things that can help your developer best understand your project and needs.
- Feature list
Any of these can help convey the idea and concept that you are wanting to develop to your developer. Of course, firms like the Peterman Design Firm has a process that helps clients define the project clearly. Every firm and developer is different too, so some of these may be better than others and some may require something completely different.