Lamport's book lists various
parameters for the layout of list (things like \topsep,
\itemsep and \parsep), but fails to mention that they're set
automatically within the list itself. It works by each list executes a
command \@list<depth> (the depth appearing as a
lower-case roman numeral); what's more, \@listi is usually reset
when the font size is changed. As a result, it's rather tricky for
the user to control list spacing; of course, the real answer is to use
a document class designed with more modest list spacing, but we all
know such things are hard to come by.
There are packages that provide some control of list spacing, but
they seldom address the separation from surrounding text (defined by
\topsep). The expdlist package, among its many controls
of the appearance of description lists, offers a compaction
parameter (see the documentation); the mdwlist package
offers a \makecompactlist command for users' own list definitions,
and uses it to define compact lists itemize*, enumerate* and
description*. In fact, you can write lists such as these commands
define pretty straightforwardly - for example:
\newenvironment{itemize*}%
{\begin{itemize}%
\setlength{\itemsep}{0pt}%
\setlength{\parsep}{0pt}}%
{\end{itemize}}
However, both packages offer other facilities for list configuration:
you should certainly not try the "do-it-yourself" approach if you
need a package for some other list configuration purpose.
If you want to adjust \topsep, the most sensible approach (at
present) is to define your list 'from first principles' using the
\list command; its invocation is
\list{<item stuff>}{<list stuff>}; the
<list stuff> is executed after the
\@list<depth>, and can therefore be used to adjust
all the parameters, including \topsep.
An alternative is to redefine \@list<depth> (and the
size-changing commands that alter \@listi), but this is not
recommended unless you're building your own class or package, in which
case one hopes you're capable of analysing the way in which the
standard classes do things (as recommended in
writing your own package).