One way to set a plane iron is to hold the plane upside down, with the sole at eye level, and point it toward a light source.
The sole will be gleaming like ice on a lake. Begin cranking the knurled knob that controls the depth of the iron. At the first appearance of any kind of shadow on the sole, stop moving the iron.
It is difficult, I think, for the first-time user to understand how little of the iron should be exposed for an optimum cut. In fact, I've gotten into the habit of lowering the iron until the shadow appears, and then raising it up half a turn or so.
Be certain the iron is raised square to the sole; this adjustment is made with the lever on the top of the plane.
When you think the iron is properly set, try it on a decent-size piece of scrap. If the sole skates across the wood without cutting, then of course the iron needs to be lower. If you feel like you're pushing a chest of drawers across a rug, then it's too low - or it's not sharp.
You want to see a ribbon of wood come gushing out of the throat of the plane like the foam that precedes a gentle ocean wave. It should be so thin you can read a newspaper through it. Producing it should be almost effortless.
If you get something between this and nothing at all, the problem may be that you're working against the grain of the wood, which can produce tear-out. Turn the board around and try again.
Seeing that ribbon of wood come out of the throat of the plane is one of the most magical things in woodworking. I never get tired of it. When you get really good at it, the ribbon should be as long as the board when you uncurl it.
I keep one of those cheap votive candles near the work bench, and when there's a lot of planing to be done, I wax the sole of the plane by rubbing it quickly and lightly with the candle.
There is, unfortunately, more than this to proper planing. You have to be careful not to take more off of each end of the board than the middle, which can happen very easily.
To avoid this, you have to learn to establish a certain rhythm. You must lean heavier on the forward knob of the plane at the beginning, even the pressure as the rear handle moves over the work piece, and shift the pressure to the rear handle as the front knob passes the forward end of the work.
Squaring the edge of the board adds another problem: keeping the plane absolutely level. This can often be ac-com-plished by holding the forward edge of the plane instead of the knob, and using the knuckles of the forward hand - your left hand if you're a righthander - as a fence running along the face of the board.