I believe it depends on the variety. Post and someone can tell you what to
do with yours. Where this is required, I believe that you look for the main
stem, the main branches and then additional stems growing in the "angle"
between the stem and branch - it is these additional stems that are picked
off.

Of course I may be doing it all wrong, in which case someone please "yell"
before I decimate my tomatoes!

Paul DS.