Here's a very basic way to see this easily: this
This is Action, search for the "Abbreviated Action": http://en.wikipedia.org/wiki/Action_(physics)search for the "Abbreviated Action", and it has the SI unit of Joule-second. This is the equation that Planck (and later, Einstein) used: "E=nhf" $$E=nhf$$ for (n=1,2,3...$n=1,2,3...$ and f$f$ in frequency, in unit of 1/second). This
This means that the Planck's constant has also an unit of Joule-second, therefore, you can interpret "nh"$nh$ as the Action of the system (since "n"$n$ is dimensionless, it will maintain the unit, and it is only used to give the "correct" answer, since not every mechanical system has "h"$h$ as the Action, "n"$n$ should be used).
So So "nh=integral(p)dq", which$$nh=\int p\,dq$$ which is the Sommerfield rule for quantization. This is just an intuition of how it works.