I thoroughly document what client's goal is. I ask questions and make suggestions so that the final deliverable is aligned with the expectations. I also mention any sort of trade-offs, if its there, to set the right expectation. I follow the following SDLC process.
Requirements gathering & the setting of critical dates for milestones & final deliverable.
Building all the features mutually agreed upon in the SoW for the project.
Once the development is complete in UAT servers a detailed QA is done.
When full review is completed in UAT & a sign-off is shared, final deployment is done.