A common mistake concerning the majority of shavers is that they tend to shave against the grain, especially on the neck area. Shaving against the grain increases the risk of ingrown hair and razor bumps. In order to know your grain direction, just feel it with you hand or analyze your face in a mirror. Shaving with the grain gives you a smooth sensation, with a specific “smooth” sense. If you pass against the grain, you will have a different feeling. You will, even, feel the "Tug and Pull" effect on your hairs.
When you master shaving with the grain, you can then shave across the grain and against the grain (in a second and third pass).