Two good books

1. "The Probabilistic Method", by Noga Alon and Joel Spencer
This is a quite useful book; you might find techniques in this book
interesting; and it is well written;

2. "The Discrepancy Method", by Bernard Chazelle
It is a more specialized book, also a little more mathematical.
I like the "Discrepancy" techniques in this book.

Mathematical Writing

http://www.betterwritingskills.com/

*Reading, Writing, and Proving: A Closer Look At Mathematics*
/Undergraduate Texts in Mathematics/
by Daepp, Ulrich.; Gorkin, Pamela.

http://tex.loria.fr/typographie/mathwriting.pdf
http://sokocalo.engr.ucdavis.edu/~jeremic/UsefulReadings/mathwriting.2up.pdf
http://www.mit.edu:8001/people/dimitrib/Ten_Rules.pdf
http://www-cs-faculty.stanford.edu/~knuth/papers/mathwriting.tex.gz
http://www.ams.org/notices/199705/comm-halmos.pdf
http://www.library.ubc.ca/scieng/aleteia/Technical_writing_with_Mathematics.html
http://www.math.ohio-state.edu/~goss/hint.pdf
http://www.fbe.deu.edu.tr/tavsiyeler/A%20primer%20on%20mathematical%20writing%20by%20Steven%20L.%20Kleiman.pdf
http://www.math-info.univ-paris5.fr/~ycart/writing/hwang.pdf