Fast at the start, slow and careful where it counts, and in the client's name from the first day.
One conversation with the people who will use the thing, not only with the people who sign for it. Then a written proposal: what we will build, what it costs, what date it is usable, and what we need from you. If we are the wrong firm for it, the proposal says so.
The first version runs on real infrastructure with real accounts and a real rule set, used by a small group at one site. It is small on purpose. Everything after that is widening, not rebuilding.
Scope rules, audit, exports, offline behaviour, the second language, the hundredth site. This is the slow part and it is where a system either becomes national or quietly dies as a pilot.
We watch it, we are reachable when it breaks, we change it when the situation changes, and the client gets a monthly report of what happened. A system nobody operates is a system nobody trusts.
Most systems that fail in this region fail for one of these four reasons, not for a technical one.
A paragraph about the problem is enough to begin. The proposal follows within a week.