Flexibility: no matter what great lesson plans a teacher has come up with, he/she needs to be able to/willing to drop or change them as soon as he/she notices it would help the pupils.
Knowing what pupils need: a good teacher has different ways of finding out what his pupils need to reach the required level. This can be done by different ways of testing or interviewing the pupils. Of course, a certain level of experience also helps.
Communication skills  (a : being able to communicate clearly with your pupils about what the lesson goals are is very important. If pupils do not know what they are doing or why, teaching goals will become much more difficult to reach.
Self evaluation skills: a good teacher often stops to evaluate his/her own actions.
Love for the subject: pupils know whether their teacher is truly enthousiastic about a subject. Seeing someone being truly interested in a certain topic helps them to start investigating it themselves.