There are three general rules regarding blood stain evidence that the forensic nurse must take into account.
First, spots of blood may be examined to determine the direction and pattern that the falling drop has produced. The shape of the spots may allow the investigator to estimate the velocity, angles and the distance from the source. The sharper end of the blood spots points to the direction where the blood has come from. If the diameter of the blood spot is unrecognizable, the distance that the drop has fallen is greater than 5-6 feet. Blood spatter may also give information about how many times the victim was struck and by what.
Secondly, the degree of spatter of a single drop of blood depends greatly on the smoothness of the surface where it lands than on how far the blood has traveled. If the surface where the drop lands is coarse or rough, the drop is likely to be ruptured or further spattered.
Lastly, the character of a bloodstain, made by drops or smaller droplets or by larger quantities of blood up to several ounces, may reveal movement at the moment of initial staining or later if a body or other stained surface is moved from its original position.
(Fisher, B., (2004), Techniques of crime scene technician, 7th edition, pg. 201.)