Most implementations start by selecting a platform and then bending the business to fit it. The reverse works far better.
Step one is always mapping the real process: how enquiries arrive, who touches them, where decisions happen and what occurs when things stall. Without that, configuration is guesswork.
The second common mistake is too many mandatory fields. Every extra field reduces adoption. Less data that is actually captured beats more data that is not.
Finally, rollout does not end at go-live. The first four weeks of real use produce the most valuable tuning signal.