Working in the UX and design field both at agencies and for clients, I have learnt some lessons that I try to stick to in each of my projects. The most important lesson has to be that design is a collaborative process. This is absolutely true and while there are times when I like to lock myself away to work on a UI design, this is best left until the final details. At the beginning of a UI design project, I work on interviewing potential users, working with stakeholders and collecting as much feedback as possible about what problem I am trying to solve.
The next piece of advice that relates to this is to create work processes that allow for you to incorporate feedback quickly. Read up on lean design principles and you will find that mockups are often the most flexible mediums that you can work with on a UI design project, for the main reason that everyone can contribute and provide feedback easily. Mockups can also be edited much faster than other forms of UI design.
The third piece of advice I would give is to create a detailed specification document with all the information about the UI design that your team members and your clients may need. Your clients will feel more confident having a document they can rely on and the rest of your team will have a clear guide for how the UI design should be. Ensure that you consult with developers, designers and UX experts when making the specification document. Often at this stage, many problems are addressed, which saves time during implementation.