You will find the bsic regulatory requirements in your national authority's documents (FCL-2 etc) however, I would say the key requirements for a successful transition are:
A simulator
Well written two crew SOPs and checklists
Well planned LOFT exercises monitored and debriefed by:
A trainer well versed in CRM facilitation techniques
Crews who are motivated to adopting the concept
It is particularly difficult to make the transition when using the same type (a contractural/regulatory change, for example) but should be easier with a new type.
Make sure the SOPs fully incorporate the Co-pilot duties and that he is an essential member of the crew; not the clerk!