I am by no means an expert in rocket stoves, but just in case we don't have a rocket stove expert here, I'll offer what I know.
While rocket mass heaters have become popular in the USA as an efficient way for hippies in cob houses to stay warm with very little fuel, they originated as a way to cook when wood fuel was scarce.
The basic principle is this: use the draft created by hot exhaust in a chimney to suck lots of fresh air in to the fire. The chimney is insulated and gets very hot, which helps burn more of the gases of combustion, producing more heat from the same fuel.
The cooking pot sits directly over the chimney, so the hot exhaust hits it directly. You can also add a skirt around the pot, so the exhaust gas is held close to the sides of the pot, further improving heat transfer.
To create a functioning rocket stove, you need an insulated J-shaped chimney. Like this:
You can add a second 90-degree bend to make the whole thing U-shaped, but the chimney must be much longer than the fuel end, so it will draw the exhaust in the right direction.
You asked about principles, and one is that the bend to the chimney should be sharp, not a gentle curve. This will create turbulence that will mix the gases and air for better combustion.
You have to get the chimney hot to make it work. One way is to light the fire in the chimney, then start adding fuel the regular way.
You can use just about any found materials that can tolerate the heat and provide insulation where needed. Here's a good Instructable you can follow to build one out of soup cans. That's a good place to start to get a feel for how these things work. http://www.instructables.com/id/How-to-make-a-Rocket-Stove-from-a-10-Can-and-4-So/
Also, be sure to check YouTube - lots of videos there.