Build the judgement behind the model.
A useful model starts with a decision and a consistent dataset. Work through the measurement question, inspect the response assumptions and compare the result with experimental evidence before recommending a change.
A useful model starts with a consistent outcome and a decision it can inform. The marketing mix modelling learning path connects this idea to the assumptions, practical checks and next steps.
Work through the what is marketing mix modeling guide to check how the method behaves before applying it.
To work through the connected decisions, read B2B MMM: model pipeline without confusing sales-cycle lag and Ecommerce MMM: separate promotions, media and returns.