Any tips for savings forecasting?

Forecasts are an assumption, and whilst we know that one may end up making an ass out of 'u' and 'me', there are guidelines and tips that can be followed to make the process more accurate and less 'finger in the wind'. Nick explores this in the Market Dojo blog below. What other considerations/tips would you share? http://blog.marketdojo.com/2015/04/how-to-accurately-estimate-your-savings.html