STEP 1-Choose the number of surround speakers.
5.1 System- The basic most popular surround system includes a center channel, 2 front speakers, 2 surround speakers and a subwoofer.
6.1 System- The next step in the surround systems includes a front center channel, rear center channel, 2 front speakers, 2 surround speakers and a subwoofer.
7.1 System-The latest in surround systems includes a front center channel, 2 front speakers, 2 side surround speakers, 2 rear surround speakers and a subwoofer.

STEP 2-Choose the type of surround system.
There are 2 types of surround systems that you can buy:
Compact Speakers-Compact speakers offer good sound in a small package. They'll pretty much fit in any room situation. Their only drawback, is the lack of low end bass they produce.
Full-Size Speakers- Full size speakers give you a fuller sound, including the low end bass. The only drawback is their size, you can either get them as floor standing speakers, bookshelf size speakers, or in-wall speakers.

STEP 3-Pick your subwoofer-powered or passive?
A sub provides the rumbling bass that makes you feel everything.
Powered Subwoofer-A powered sub has a built-in amplifier that provides all the power, instead of needing an add-on amp.
Passive Subwoofer-Available but rare, passive subwoofer needs a separate amplifier or can be powered by an A/V receiver.