Discussing and brainstroming with the Product Managers and stakeholders the product in terms of the product's value propositions, what is a must-have in the product, and what's nice to have. Start sketching a concept sketch for main screens (low-fidelity) on paper to imagine the main components and general flow.
Focusing on researching competitor apps/products and how they handle related features to understand what are the current design trends in terms of User Flows and UI elements. And collecting screens and inspirations to create a moodboard for the product
Creating User Personas, User Stories which are useful for designers to help understand the product/service interactions from the user's point of view, and Storyboarding to connect personas to their user stories to cover as much scenarios as possible.
Going for a round 2 with low fidelity wireframes, then connecting wireframes in a clickable prototype to validate the interaction experience. Creating high fidelity screens with actual UI components, colors, and elements following a design system and creating any new needed assets(icons, graphics, backgrounds).
Do quick testing sessions on the product with colleagues and friends to make sure the experience and UI elements are all clear and working as they should. Then do user testing session with our target audience, surveys, and finally some analytics to gather Quantitative data on clicks, and actual user interactions in the product.