Here are dirty hacks for page layout in LaTeX and a few useful standard settings.

I load the following document class:

\documentclass[bibliography=totoc,12pt,a4paper,headsepline]{scrbook} 

The option bibliography=totoc puts the bibliography into table of contents. The option 12pt sets normal font size to 12pt instead of the usual 11pt. This font size was a requirement for my thesis. The option a4paper sets DIN A4 paper (which should be the default anyway). The option headsepline adds a line below the header content on pages without a title.

A useful additional option may be oneside, which creates symmetric margins for one-sided print. Again, that was a requirement for the manuscript of my thesis. For the final print, I needed a normal two-sided print. A useful option there is titlepage=firstiscover, which gives equal margins for the first two pages (the book cover).

Usually you don’t want to tamper with the margins that LaTeX gives you. But in some cases, you may have specific guidelines that you need to adhere to. Or you have a fixed number of pages and run out of space, so you want smaller margins. Anyway, this is not recommended, I am just showing you how it works, because I can.

We have loaded the documentclass scrbook which is the KOMA-Script document class for an DIN A4 page book with a font size of 12pt. At that paper and font size, KOMA-Script uses a value of DIV=12 to calculate margins and text area sizes. The page has a width of 157.50mm and a height of 222.75mm for the text area. The top margin is 24.75mm and the inner margin 17.50mm. You can increase or decrease the margins by setting a different DIV value. So if you use the option DIV=13 for example, you will have a bigger text area (161mm wide instead of only 157mm). You can play around with the values until you find something you like. Here are the measurements for different DIV values for an DIN A4 page:

If you don’t find anything you like, you can set all values by hand with the geometry package. Use at your own peril. This is an example with a larger text height:

\usepackage[width=157.50mm,top=35mm,left=24mm]{geometry}  % gives textheight=226.36mm

When you play around with margins and text area settings, the package showframe is useful to see what you are doing:

\usepackage{showframe}