My coach tells me that my communication skills are lacking on the field. Communication on the field is extremely important at all levels of soccer.
Good communication is crucial to any team that wishes to succeed.
Your coach probably feels that you need to communicate with teammates more on the field, or that you are communicating incorrectly. If your coach feels that your lack of communication is the problem, then simply talk more on the field when you feel your teammates need your assistance. Your teammates may need your assistance in a number of ways because you act as an extra set of eyes for them. Speak loud and clear enough so there is no doubt whether or not your teammate hears your instructions. Also, soccer can be a very fast-paced game, and you should keep things brief so your teammate can react immediately to the situation at hand.