Titus, Unity and John E are all correct, and to a certain extent incorrect as well.
There are several varibles. But it really is not trial and error, nor is it guessing. Actually the meter if used properly will get you spot on for EXPOSURE. But the finer points of color, contrast, speculiarty and several other factors all with experience or taking a really good studio lighting class.
The type and style of lighting determine the way you use the meter. Some styles like Rembrandt, Butterfly and ring all use the meter facing toward the camera. Short, long or backlit may require using the meter toward the fill and then main to determine the split and make the "proper" exposure that way. Rim and sillhouette use the meter off of the backside of the subject and then off of the fill onto the subject to get it right.
Every photographer develops little cheats that they use, metering off of foamcore or an 18% grey card for some lighting styles. Highlights, negative fill, hairlights, and background lights all meter differently as well. You cannot do studio strobe lighting without a meter, unless you like excersises in frustration. You need a base constant to start with, then you calibrate your meter for the style you use most. Color of skin, hair and outfits may require some compensation to get the tone and color right (as opposed to "correct").
The best suggestion is for you to get into a studio lighting course to learn the in's and out's of exposure for studio use.