Set your acetylene regulator to 8-10 psi, oxygen to 30 or so. Crack the acetylene valve, light the torch. Open it until you have a strong yellow flame that does not give any soot. Slowly open the oxygen and "walk" the flame back to the tip. You want a neutral flame with clear and well defined jets.
Preheat the edge of your steel, you don't need to preheat to much. Rookies try to get a big red hot preheat. You just heat the edge up to where it starts to yellow and throw sparks.
Keep your torch tip about 1/8" above the surface of the steel.
Hit your cut lever, you should see a nice stream of molten steel jet through the edge. Slowly move the torch in direction of the cut, keeping a steady stream of cut flowing from the backside.
Torch speed is the key, too slow and you just make a blobby cut that seals back up with slag and you overheat the workpiece, too fast and you outrun your preheat and lose the oxidizing jet which is what actually does the cutting.
If cutting a straight line is tough, clamp a piece of angle iron to your workpiece to act as a fence.