Most beginners make the same common mistakes.
The most common are poor stances, open centers, off center positions, stiff arms, inconsistent forces, and in general, poor form. Beginners often feel these elements are not important, yet it is these things that result in their defeat. The photos below show the difference between a poor Wing Chun stance and a good Wing Chun stance. You should feel solid as if sitting on a high stool. Also, you should feel your weight distributed evenly along your legs.