In my experience, cuts and nicks occur for only a number of reasons.
First off, as mentioned above, the razor is not sharp enough. When you use a razor that is not sharp enough, it tends to hang up and pull and struggle through the stubble. This in turn leads the shaver to use more pressure than is necessary, or to hack away a bit with the blade, and increase their chance of nicks and cuts.
Secondly, technique (assuming the blade is shave sharp):
(a) The direction of the blade as it moves across the skin should be generally perpendicular to the spine. Lateral movement of the blade parallel to the spine should be avoided at all costs, particularly when you first start out. People talk of a scything motion with a straight - I would avoid that to begin with. It is a slightly more advance stroke for slightly more advanced users.
(b) Blade angle is important - a steep angle will increase the chances of cutting yourself.
(c) The movement (or lack thereof) of the blade on the skin is also a factor with nicks and cuts. I find it best if the blade is in motion just before it touches the skin, and remain in motion until just after it leaves the skin. A shortish, deft stroke minimises the risk of nicks and cuts - try to avoid stopping to adjust hand or arm positions, or modify or adjust your grip, when the blade is on your face. This is the one that always gets me - I get overconfident and change hand position on the fly, or modify my grip halfway through a stroke, and the next thing I know I have a 3 inch cut. Just take the blade away, do your adjustments for the next stroke, line it up off your face, and then decisively shave that bit. It might seem a bit start/stop to begin with, but pretty soon it becomes second nature, and it starts to become a part of your natural stroke.
Don't be afraid to develop a "buffing" technique with straights. It might look a bit dangerous, but nothing could be further from the truth. Just lock your elbow and move the razor from the wrist in shortish strokes to start, and progress to a more buffer-y effect as you gain confidence. I can say with absolute honesty that I have never nicked myself while blade buffing. It is on those longer, less controlled strokes that I tend to come undone if not careful.
(d) Stretching. Stretching is quite vital with straights. This is not just so that you get a close shave. It is also a way to avoid nicks and cuts: a nicely stretched, flat surface will be a lot easier and safer to shave with an open straight edge than a bumpy or loose surface. Again, make sure that the area to be shaved with a particular stroke is well-stretched beforehand, and the stretch held throughout the stroke. Don't go adjusting the stretch halfway through a stroke. :eek:
Anyway, sorry for the verbal diarrhoea. Its just that I have held numerous inquiries into my own cut and nick events and thought I would pass on the results... YMMV :D
I'd generally also say that a healthy respect for the blade does not go amiss. Not fear, but respect. It is usually when I start taking my "mastery" for granted that my razors bite me.
James.