Measure what can be measured, and make measurable what cannot be measured. Galileo Galilei
For each of your marketing activities, what does it cost to generate a warm lead for your organisation. If you invest £5000 on a poster campaign and it results in 25 enquiries. The cost per lead is 5000 divided by 25 which is £200. Not only a great way of measuring how effective an activity was but also a simple way of comparing the effectiveness of different actions.