I don’t always follow the same story splitting approach when I need to split a story. It has become intuitive for me so I might not be able to write about everything I do or what goes through my mind or how I know.
Splitting user stories is always a tough topic for new teams. If teams are used to working in tiers, then this is a completely different way of thinking for them. We are looking to split stories into thin slices, not complete a tier at a time. As Andrew hints at above, this is also a bit of an art form. It’s something you develop and get better at over time as you learn to look at the problems differently. In the mean time, you have to constantly challenge yourself and ask how can this be broken down further. I encourage you to check out his post for some good tips, also check out my previous posts on the same subject: How You’ll Probably Learn to Split Features, Breaking Down User Stories – When versus How.