For beginners i recommend:
The Theory of Poker: A Professional Poker Player Teaches You How To Think Like One
[ame="http://www.amazon.com/gp/product/1880685000/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687682&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=1886070253&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0SC92ZMRJR6N4JZ1PJ8S"]The Theory of Poker: A Professional Poker Player Teaches You How To Think Like One: David Sklansky: 9781880685006: Amazon.com: Books[/ame]
It is a investment!
or you can study in sites like: pokerschool and intellipoker