The following ideas are taken from Alan Perlman's excellent
book "Writing Great Speeches". In it he makes very simple, but
useful suggestions as to how to change between registers when speaking.
Native speakers of English probably do all this already without
thinking about it, but it will be useful for those of you with English
B to see a few "tricks" that you can use.
The basic suggestion is that if you wish to be more formal in your register you
should use a more impersonal language when speaking, and if you
want to be less formal, a more personal one.