Develop a strong evidence base

Legitimacy is essential - does your evidence come from technical expertise and/or representative experience?

Do you need to commission some research or do some research yourself?

Are there other sources of information / statistics you can draw on?

Make sure your research is relevant e.g. you need Welsh statistics for a Welsh campaign

Try to locate case studies and real-life examples - these can be extremely powerful and can be more likely to be picked up by the media than dry narrative.