Content (or What do we know?)
CELTA doesn't teach us grammar. CELTA instructors understand, quite rightly, that they cannot possibly address all the content in the short four weeks of a full-time CELTA course, so grammatical education is mostly left to the students. This means that most graduates, when they first step in front of their classrooms, usually only know as much as they prepared the night before. The usual course of action for these teachers is to look for textbooks, worksheets or online resources that will provide students with enough examples that they will understand and begin to control the actual teaching point. Lacking content knowledge, many teachers handpass the teaching authority to the textbook or worksheet. The article by Thornbury and Meddings, two respected writers in the ESL field, is enlightening.
Methodology (or How do we teach it?)
There are several teaching methods that most teachers have grown up with, learned about in CELTA courses, or have seen their peers and colleagues practise. We lecture (teacher-centred), allow the students to work it out themselves (student-centred) or use a teaching device such as a textbook, website, worksheet, DVD, CD or Smartboard that mixes the two.