Figure out where you have common ground. Do you agree what problem you’re trying to solve? Do you agree on how you know this is the right problem, and the data/research informing your strategy? Do you agree on how you will measure success? Before getting bogged down in specific implementation details, ensure that you’re aligned on the larger questions motivating each of your perspectives.
Show the hiccups and messiness. Experienced designers know that no project goes smoothly, and they’re not afraid to talk about why. Fresh designers think that perfection is ideal, so you may be tempted to edit your work to hide the messiness. Don’t. Be open about the chaotic process that is design. Everyone runs into hiccups and messiness.