What do people think are good economic policies to reduce informality? It seems that lots of informality, ie. people or firms that exist without being part of the tax, health, legal, regulatory systems, is one of the main issues to deal with in developing economies or poor parts of developed economies. Is there some sort of consensus on how to reduce informality?
Three part answer:

Causes:


Trust in the system (particularly trust in politics)
Attitudes to risk (i.e. being caught)/Enforceability of regulatory power
Education levels
Economic empowerment/unemployment/low wage level
Law of unintended consequences 
Cultural considerations
Geographical considerations


Reduction:


Political corruption cleansing
Tighter regulation on informality 
Greater communication and transparency
Demand and supply side policies


Evaluation:


Extent to which informality is a problem
'Trickle-down' effects
Ease in assessing magnitude of informality