Yes, and not only the first time is difficult. It is always difficult for me to determine what exactly is worth writing about myself and what information needs to be kept silent. In general, I have problems with such a definition. In general, I believe that it is better to trust specialists to write such important matters - for example, in the center of the online resume service they will approach your question with all their hearts and help you determine the right direction in which it is worth emphasize your main advantages. And you will be satisfied, and the employer is more likely to respond.