I agree with Pohnpei - most rape is about power and domination, not about sex. However rape is also often a crime of opportunity, which means that the rapist generally acts more or less on impulse, choosing a victim who seems available and vulnerable. While the victim is NEVER to blame, women can and should be aware of situations in which they are at higher risk, and take steps to avoid these when they can. In most cases this has more to do with location than with clothing, though. Women need to avoid being in isolated locations with a potential rapist, and they need to avoid becoming drunk or high on drugs in a situation where rape could occur. Because of the prevalence of rohypnol and other "date-rape drugs", many women's self-defense classes now recommend that a woman out on a date or at a party or club should never set her drink down or drink anything that is handed to her by another person. It's sad that women must go to such lengths to protect themselves, but it is important that they do so.
Those who rape children are psychologically ill. For them, too, rape is a attempt to exert control and power over the victim. Pedophilia is virtually impossible to treat, and in a great many cases the rapist was once a child victim, so the cycle goes on and on. Most pedophiles use shame and threats to keep their victims from revealing what is happening, so the victims do not get the help and support they need.