Use data to justify design. The trend of “data-backed design” is nothing new. After prioritizing a mobile project it is important to track mobile KPIs. For retailers, monitor Average Order Value (AOV) and the exit rate on the page where the checkout funnel begins. For lead generation companies focus on CTR of the primary Call-To-Action button and the lead to close ratio (successful sales / number of leads * 100). If you have a travel site, focus on return sessions (customer retention) and channel-specific traffic (ie: are social shares increasing). Consider monitoring micro conversions as well like email newsletter signups, comments on an article, user reviews, video views, or shares on social media. Pro tip: I highly recommend you leverage this brilliant Datastudio dashboard that one of my peers (Damla Cakirca) made to monitor user engagement on your site.