A journalist is generally understood to be one who communicates objective truth about current topics to an interested but critical audience. A good journalist is one who realizes that the objective truth is unobtainable.
A journalist must understand the medium he works in. For instance, a newspaper reporter will write in correct English.
An excellent journalist will take the extra step for professionalism in reporting, with consideration for truth, fairness, balance, decency and ethics. He will spend many hours researching his subject of choice. If you cannot do this, you might not be a successful journalist.