I think that slap's answer contains much wisdom (as in what law are you working to enforce), but another component is an awareness of the culture you're advising (to including its history and customs when it comes to law and law enforcement). The US model is a poor one to export anywhere, because it is so deeply based on our rather unique structure and systems. Tom makes that point well, and also points out that the First World clarity between military activity and law enforcement is often absent in other regions.

As I recall, the RCMP was created to conduct what could be called "distant law enforcement" in regions that might not yet have any local government. A good US analogy might be the early function of the US Marshals, although that was often clouded at the marshal level by political appointees and such. The Texas Rangers also come close, but again their roles blurred in places and often crossed into purely military functions (the Red River War in 1874 provides some examples of this). The State Trooper model also breaks down to a degree, because each state maintains its own organization with varying levels of investigative power.

Law enforcement is pretty specialized work, and it becomes even more so when you have to tailor the package to fit the environment. The gendarme/constabulary model might be best for this, as it would be most open to changes and expansion or contraction depending on the local situation. It's clearly something that should be a dedicated function, possibly at the NG or AR level as Ken mentioned (although I also think it's something that should be multi-national whenever possible...at least in the planning stages).

My preference would be to go in with a gendarme model in hand, adjusted to fit local conditions and needs. Part of that package would be the development of local (village-level) forces to augment the larger structure (based on the nation or even provinces if necessary). Before deploying that, there would need to be agreement on the laws being enforced (as slap mentioned), as well as a tailored IO campaign to get the locals acclimated to the "new sheriff in town." This would require some advance planning (something we seem to be spotty at), and a willingness to adjust on the fly to remove things that don't work and add in elements brought in from the field (something we have been good at). As the local gendarme units become capable, we should phase out direct involvement, possibly refocusing at the local level if needed to make sure that the second level of "folks in blue" actually makes it to the streets.

Random thoughts, which might become more coherent once I have more coffee....