Stucco cracks on the outside of a home are typically mirrored with the drywall cracks that appear in a home. The most common areas that they will show up is around door ways and windows. The reason being is that these areas have the easiest ability to move within a home's framework. Moving around a gap is a whole lot easier than moving within a portion of a rigid wall.
Now depending on the type of stucco finish that you have you may notice more cracks than other. Smooth finish stucco will show way more cracks within the stucco than you other rougher finishes of stucco. The reason is that the rougher finishes have a lot more "cushion" to absorb and hide some of the cracks. They are more than likely still there, but just haven't reached the surface to be noticeable yet.
The reasons that stucco cracks are all of the same reasons that the interior drywall cracks. You can view that list here. Stucco cracks don't always mean that your foundation is moving and most of the time it is a result of some other underlying factor or reason.
We inspection thousands of homes every year. Our number one goal is to always find the reason your home is experiencing things that you are noticing. Just merely fixing a stucco crack or drywall crack does no good if you don't find out "WHY" it happened. Otherwise, 9 times out of 10 you will be repairing the same area on a regular basis. Contact a qualified foundation repair inspector to provide you with the why and then you will be able to better make a decision on an effective fix.