\layout command which draws a diagram of your existing page
layout, with the dimensions (but not their interrelationships) shown.
Even changing the text height and width, \textheight and
\textwidth, requires more care than you might expect: the height
should be set to fit a whole number of text lines (in terms of
multiples of \baselinskip), and the width should be constrained
by the number of characters per line, as mentioned in
“changing margins”.
Margins are controlled by two parameters: \oddsidemargin and
\evensidemargin, whose names come from the convention that
odd-numbered pages appear on the right-hand side (‘recto’) of a
two-page spread and even-numbered pages on the left-hand side
(‘verso’). Both parameters actually refer to the left-hand margin of
the relevant pages; in each case the right-hand margin is specified by
implication, from the value of \textwidth and the width of the
paper. (In a one-sided document, which is the default in many
classes, including the standard article and report
classes, \oddsidemargin stands for both.)
The
“origin” (the zero position) on the page is one inch from the top of
the paper and one inch from the left side; positive horizontal
measurements extend right across the page, and positive vertical
measurements extend down the page. Thus, the parameters
\evensidemargin, \oddsidemargin and \topmargin, should
be set to be 1 inch less than the true margin; for margins closer to
the left and top edges of the page than 1 inch, the margin parameters
must be set to negative values.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=marginmanual