Examples

IFRS

All our forecast models follow these rules:

Ensure that the assumptions used are in line with the existing drivers underlying the business or that changes are justified.

Aim for one assumptions sheet. Clients should be able to change assumptions easily.
The first sheet should be either a sheet index or a diagram or a text guide explaining how the model works.
Write up the assumptions. They may be part of a business plan but there should always be some words to explain what the model says.
Input cells should be coloured, eg blue for input, black for fixed. There should be a key to explain this.
There should be monthly and separate summary sheets.
Show file and path name.

Wherever possible, use client nominal codes.
Be rigorous in setting up formats so that they are exactly the same as actuals, eg can we paste actual P&L information and derive actual balance sheet by flexing assumptions?

Consider re-organising clients nominal ledger or re-organising the report so that costs are grouped logically eg marketing, premises, admin, finance.
Make sure workbook can be printed on A4 and easily read.
Make sure it looks good. Make sure the summary page gives an immediate, clear understanding of volumes, prices and financial results.

Include a sheet for version control. Models should be numbered sequentially NOT dated. Version control should indicate if the version is completed and what the main changes were.
Avoid hiding rows, columns or sheets (we all sometimes hide a payroll sheet).
Avoid external links.
Avoid long or similar sheet names.
Never mix formulae and values in same cell.