[plt-scheme] Scheme rules of thumb

Hi,

I'm rather new to scheme and I'm having a hard time
designing and laying out my program in a "schemish"
way.  I was wondering if there are any "rules of
thumb" that you guys follow when writing programs. 
Some examples from other languages:

This is an actual rule but a helpful one from Java. 
One Class per file and name the file the same as the
Class.

I remember reading in a Smalltalk book that you should
keep methods under 20 lines of code.  Anything more
than that should be broken up into multiple methods.

In Ada, although pointers are available, there is
probably a better way to do it without them.  Don't
just jump in and start using pointers like you would
with C.


Do you guys have any things like this that you follow
for scheme?  How do you organize your modules?

Thanks,

=====
Kevin Hostelley