Most importantly, and alas something rarely stated on enotes, a good lecturer should be an active scholar with exhaustive knowledge of the field, who is engaged with current scholarship, and him/herself actively making new and valuable contributions to the field.
A lecturer is not just a receptionist who needs a nice personality, or someone with some education department theories about pedagogy, but a working scholar sharing knowledge.
Lecturer in North America means an instructor who is not tenured or tenurable and often on a temporary contract (tenure stream titles are Assistant Professor, Associate Professor, and Professor). In British universities, lecturer is the first rank an instructor holds after obtaining the PhD. In Britain, teaching stream instructors can move on to "senior lecturer" and research oriented ones to "reader" or, eventually, "professor".
In some countries, "Lecturer" means something like "Professor" does in the USA. Even in the United States, some departments use the terms interchangeably. So obviously, if you mean that more specific term, a Lecturer in English would need a PhD in that subject, and in this day and age, would need to have written a strong dissertation, and, as others have said in this discussion, be an expert in their field.
More generally, a good lecturer understands the balance between speaking to the whole class and connecting with individuals. This is difficult, but if lecturers don't do it, they're not reaching their students. Soliciting questions, calling on students, coming up with interactive activities, and using multimedia are all hallmarks of an effective modern lecturer.
A lecturer of English would likely need to be a good speaker. The person would need to enunciate and use proper English grammar while speaking. The person would need to be able to organize and deliver a lesson verbally as well as create visual aids to assist students during the lecture. This person would need to be well versed in the topic they were presenting in order to help students understand and answer student's questions.
Such a person would need good people skills and good organizational skills. They would need to interact well with people as this is an important part of being a teacher. Good organizational skills are important both for teaching and for conducting academic research.
Lecturer doesn't mean a guide, instructor or entertainer., he/she ought to possess great knowledge in related subject., and must be able to explicitly express what he actually wants to say...