The guillotine was used during the Revolution in the same way as the lethal injection or the electric chair was used in the 20th century. It was not a weapon used to target nobles in general. It was used from 1791 until the abolition of the death penalty in France to execute anyone who had been sentenced to death by a court. The exception to the rule was military tribunals, since they could sentence people to death by firing squad, but the sentence didn't vary because of the class of the condemned person.

The people who were sentenced were already prisoners before the trial. Unless the execution was delayed, the condemned would be taken from the jail to the place of execution as soon as possible. Speed was important, because the period between the sentence being passed and the death of the condemned was seen as torture. The convicted person would be transported on a cart with their hands bound, and they were escorted by armed guards.

Beyond the physical constraints and force of arms, social norms were probably also an important part of why things went so smoothly most of the time. Even if the revolutionary public thought of you as guilty, your demeanor during the execution would affect their opinion of you. Facing death with dignity was very important, and whether or not you kept your cool was seen as an a direct reflection of your character. If you panic, that's evidence of both guilt and moral shortcomings. If you don't show any fear, that could be seen as evidence that you might have been a good person regardless of your guilt. Calm was seen as an indication of piety and a clean conscience. Reputation and respect was very important to a lot of people, even after death, and that could have been enough to motivate some to go to their death without a fight.