I have never had much desire to read books about poker, but I have finally changed my ways. I have read most of your basic books in the past (Super System 1 and 2, a few of the Harrington books, and Barry Greenstein's book). I am primarily a SNG player, and in the past few weeks I have read the 3 best books on SNG/Multi-table games that I have ever read.
1. SNG strategy by Collin Moshman
This is a must-read for your typical SNG player. Very easy concepts to grip. This is a great book to get you started. It helped me plug a few leaks in my game that I have been noticing.
2. Kill Phil by Blair Rodman and Lee Nelson
Another must read for tourney players. This book goes a little deeper than the first book I listed. I would call this one another must read as well.
3. Kill Everyone by Lee Nelson
The sequel to the above. These two books tie together experience, math and even more advance strategies than your average book.
I have found that in the past few months of doing more reading that my game has evolved exponentially. You can even get the Moshman book from the Full Tilt store too (8100 FTP's).
Bookmarks