Changing staffs in the middle of the song

[Mark Dewey]

I've come across many songs where the number of staffs changes in the middle of 
the song.  How is this ideally done?  I've found a number of ways to do it . . 
. but they're not easy, ideal, or what I would call standard (not very 
reusable; pretty much, I have to spend hours finding a new way every time, 
unless I want to use multiple scores in the same sheet music).

So, let's say I start out with two staffs: one with a treble clef and one with 
a bass clef.  Then, I need to change to three staffs where the top is treble, 
with piano accompaniment on a treble and a bass clef staff below.  Then, I want 
to change to a full choir staff where each voice gets its own staff . . . And . 
. . I want to do this all on one score.

Anyway, how do I do this, normally?  Or . . . is this not a 'normal' thing to 
do?

Here's a solution I found for changing from a solo staff with a two staff piano 
accompaniment to a regular hymn-style two staff setup on the chorus:
I just didn't continue with the treble clef of the piano accompaniment, and 
then it sort of happened naturally.  However, this would definitely not stand 
up for a need for more complex staff changes (and adding multiple voices would 
be a definite problem here, and that's why I had to come up with the solution 
for my previous post).

Anyway, thanks for all the help you can offer!