Formatting Information is a beginner’s guide to typesetting with LaTeX. Expertly written by Peter Flynn, this document does not assume any prior knowledge.
www.tex.ac.uk

Tobias Oetiker teaches you how to write texts so that they can be processed by LaTeX. The scope of this introduction is sufficient to cover most applications of LaTeX.
www.ctan.org (PDF file, 2.2 Mb)