From Fancine Bates, Chief Exec of Contact a family; before I forget them:

Clarity of purpose (be very clear about what you want – all agree what it is: people will sniff out any differences)
Evidence base – justify your arguments
Identify decision-makers and target them
Find allies – don’t be oppositional
Plan but be flexible (long term strategic planning is needed)
Review goals (work out where you are and be prepared to change if necessary)
Communicate (especially if working in a consortium/alliance)
Never give up!