Financial Modelling in Microsoft Excel/Overview

Financial models need to be: This needs clear layout, good documentation, data validation & results testing.
 * useful – they need to assist the user in solving the business problem
 * This needs good business analysis and design skills
 * accurate – they must do exactly what they say they do
 * This needs correct logic, accurate calculations & relevant results
 * flexible, so they can evolve throughout the analytical process and beyond
 * provable – the inputs, calculations and results can all be verified

A good guiding rule is to keep things as simple and as clear as possible, for example:
 * using common functions rather than complex or rarely used functions
 * keeping formulae short
 * not being "clever", which may just confuse other people
 * separating the spreadsheet into clearly marked sections

Code Complete, the classic book on programming by Steve McConnell, says that managing complexity is the major imperative.