Once you have an idea for an app, the next thing to do is to translate that idea to paper. This will make it much easier when discussing with a designer in the initial build phase.
Ideally, you will want to “storyboard” or “wireframe” the app on paper. This means drawing out each app screen, buttons and then detailing what happens when those buttons are pressed. Don’t worry, you don’t need to be an artist, the purpose is just to show what the app does and how it is supposed to interact with the user. This part of the process is important because if you don’t know yourself how the flow of app is going to go, then how is the designer supposed to figure it out when it’s your idea?
Once you have the app outlined, and receive a quote for it, you need to be aware that if you decided to change things that it could affect the quote depending on what the changes are and if it adds on to the hours needed to complete the design.