Yoga Teacher Training can generally be divided into 2 parts: Basic training and Comprehensive Training. Combining styles of yoga is a growing trend. While hybrid combinations can be fun and helpful a solid working knowledge of the Basic Guidelines for Teachers of Yoga is highly recommended before cross-over teaching.
The word Yoga Teacher is free for anyone to use. There is a dramatic rise in the number of programs claiming to offer certification in Yoga Teaching in as little as a weekend of study. In turn there are yoga instructors, though they may be very good in the field, take small courses, get the certification and then go out and teach Yoga. Some may not even realize that teaching yoga is a sophisticated science that requires alot of study and experience on the part of the practitioner before they are qualified to teach. It is up to the teacher to do the research and choose a course of study and practice - hopefully which requires at least a year of study and a significant amount of studio experience before teaching your own classes. A good teacher training requires students to take regular classes for themselves, to practice teaching volunteers, and to observe and assist qulified teachers.
Teaching yoga is not formulaic. It is based on teaching principles and teachers within these develop their own format and formulas unique to them and to their students.