Sketching up the frames of your app is a great way to make it a bit more realistic. There exist several tools to develop mockups. Feel free to take a look at mobile app mockup tools and see which one works best for you.
Mockplus - A simple drag-and-drop prototyping tool and an all-in-one design platform for prototyping, collaboration, and design systems. Low learning curve and very cost-effective.
Balsamiq - Balsamiq wireframes are the industry standard for low-fidelity wireframing software that reproduces the experience of sketching on a whiteboard with the use of a computer.
Moqups - You can create a simple wireframe, solid model, and UI concepts by using this online mockup. Its built-in templates can be used directly.
Mockingbird - It offers a simple and quick approach to make interactive wireframes and models. Create and share clickable interactive mockups of your site or application.
Invision - Ability to create live prototypes from static images as well as wireframes, which, when coupled with functional facilities of the software, can be transformed into the app prototype.
Creating mockups is an incredible method to test an early form of your applicationand helps developers with their coding. It's simply an issue of coordinating the privilege prototyping tool to the right requirements of your project.