Begin by thoroughly understanding your client's app requirements, target audience, and business goals. Conduct meetings or discussions to gather information about the app's features, functionalities, and design preferences. This understanding will guide your development process and ensure the final product meets the client's expectations.

Based on the client's requirements, prepare a detailed proposal outlining the scope of work, project timelines, and deliverables. Break down the project into smaller tasks and define milestones for efficient project management. This proposal will serve as a roadmap for both you and the client throughout the development process.

Create wireframes and design prototypes that depict the app's user interface and interactions. Focus on designing intuitive and user-friendly experiences that align with the client's brand identity and enhance the overall user experience. Iterate on the designs based on client feedback and conduct usability testing to validate the UX design.

Utilize Flutter, a cross-platform framework, to develop the app's front-end. Leverage Flutter's single codebase to build apps for both Android and iOS platforms, reducing development time and effort. Implement the UX designs, create interactive elements, handle user inputs, and integrate APIs to ensure smooth functionality and a visually appealing interface.

Develop the app's back-end using Java, Kotlin, or Swift, depending on the client's preferences and project requirements. Utilize the appropriate programming language and frameworks to handle data storage, user authentication, server communication, and other back-end functionalities.

Integrate third-party APIs, such as social media login, payment gateways, mapping services, or cloud storage, to enhance the app's functionality. Use the respective programming languages and frameworks to handle API calls, data parsing, and response handling.

Conduct comprehensive testing to identify and fix any bugs or issues in the app. Perform functional testing, usability testing, performance testing, and compatibility testing on different devices and operating systems. Ensure the app meets the client's requirements, functions smoothly, and provides a seamless user experience.

Prepare the app for deployment by creating the necessary build configurations and optimizing its performance. Follow the guidelines and requirements set by Google Play Store for Android apps and Apple App Store for iOS apps. Assist the client in submitting the app to the respective app stores and handle any necessary updates or changes.

Provide post-launch maintenance and support services to address any issues or updates that may arise. Offer regular app updates, bug fixes, and compatibility enhancements to ensure the app remains secure, up-to-date, and functional. Maintain a strong client relationship by providing prompt and reliable support whenever required.