A little lubricant will make the job a lot easier.
Have you ever snapped off or stripped the head of a screw while trying to force it into hardwood?
Before screwing into hardwood you should always pre-drill a "pilot hole". A pilot hole should generally be about ½ the diameter of the screw in hard woods and ¼ in softer woods.
Sometimes even with a good pilot hole, a stubborn screw will refuse to go any further. To solve this simply rub a little moist bar soap or paraffin wax on the threads to act as a lubricant. This is especially useful with soft metal screws such as brass and aluminum.
Note: Do not use oil or grease as these products may leach out into and stain the wood.