Ask HN: What would you teach your younger sister/brother about finmod?

Say you have an younger sister or brother who is a first-time entrepreneur and would like to apply for a bank loan when there is a need in the future(Let us say that they are not very keen on venture capital). They want to have as much insight as possible into their business from the financial perspective. This is for thier own sake(e.g. to make better decision) as well as to be well-prepared for future loan application(s). What would you teach this younger sister/brother about financial modelling, forecasting and credit risk analysis so that they are able to generate their own data for analysis before making a loan application?