Windplayer if it helps as newcomer, first thing is you cannot compare how you operate a piston engine say in a DC3 with a pure turbine engine they are very different beasts. A piston engine requires a fuel and air mixture be delivered inside the engine in precise amount due to the volume of the area taken up by the pistons, carburettors and fuel injection systems do this work. On a jet engine, fuel is sprayed into a big burner or several burner cans in the front mid section and pressure changes take care of the rest, low at the front high at the back and hey presto gas flows in that direction.

The levers on the pedestal for the engine in an aeroplane like the 727 or 7-7 are of two types the power or main levers simply control fuel flow like a tap the others control fuel like a thingy on a line does. The condition lever or fuel thingy lever lets fuel flow to the engine and shuts if off to stop thats all. The power levers control fuel flow, so they are in effect like a bunsen burner, push them forward more fuel more fire bigger burn more power and that is it, the essence of simplicity like the jet engine, fans at the front compress air in to where it is burnt ones at the back and they may be several convert the hot air resulting from the fuel burning into power or thrust out the back which is why there are two RPM or N gauges on the dash. REverse thrust is just a mechanical connection that means you bring the power levers back so the engines go to idle or low rpm, then moving them all the way back directs linkages which open up the reversing mechanisms vents or doors at the back of the engine to redirect the flow forward and as you pull back the levers they add more fuel and the engines power up to a maximum again but this time the air flow is directed forwards out of the back of the enigne. In a propeller aircraft reverse thrust is achieved by the propeller angles going into a negative pitch and then the engine powering up again.

So in short there is no mixture control in a jet engine as pressures from the outside air pressure, the inside pressures of the engine when burning and turning and the fuel nozzles delivering fuel handle all that so all you have to do to go is levers forward and stop levers back, it is that simple.

Hope this helps, performance planning is another subject all together and there are some good threads on this forum and the 707 forum about fuel settings and planning to help you out.