Lead bossing or dressing?

i've been studying it for my nvq in plumbing. to p my course i'll need to do some internal corners, external corners and a chimney weathering. it's not a skill you can pick up by reading a book and my collage tutor is a p;rick and is little help. so i'm looking for anyone who has done a bit and can give me some advice and can p on a few tricks of the trade maybe even give me a few links to some good video tutorials by some experienced trades people . i've seen the ones on youtube theirs only about 3 or 4 good ones. anyone know of any more??