I would like to highlight another route that I think should be more-widely known and used as a basic starting point before anyone stands in front of a group of people and attempts to teach, train or 'instruct'. I am an ex-teacher (primary SLT) and, for various reasons, took an additional qualification a couple of years ago in order to be able to teach adults.
The FE basic qualification Award in Education and Training (AET), previously known as PTTLS, enables people to teach children aged 14 plus at instructor level. This is a Level 3 qualification.
The course is a few hundred pounds and can be done part-time, over about 10 weeks, at an FE college. It is 'teaching 101' and covers the basics of:
Teaching and learning
Assessment
Inclusion
Differentiation
Equalities
Record keeping
Behaviour management
Planning schemes of work
Planning individual lessons
As an experienced teacher I found it all straightforward, but noted that it is actually quite a good overview of what the role and responsibilities of a teacher involve - yes, you do need to include everyone; yes, it is your responsibility to adapt what you are teaching so that everyone can learn; yes, you do need to assess progress on a regular basis. So many people have misconceptions about what the role of a teacher involves due to the changes since they were at school, or having been educated elsewhere, or simply having different philosophies around what it means to 'teach'.
I would argue that any person, expert in their field or not, should have at least this course before they step into a classroom. I would also recommend it to anyone considering a PGCE or other form of teaching training as a cheap/quick way of finding out if they really want to do the job.