here is something that will really assist you once you grasp it.

it looks a lot better in color...but this is an ascii medium...:-)

---------------------------------snip and save-------------------------------
                        Chord Subsitution Examples
                         (770) 979-7958   date:  930128
                           michael_rhine@mindspring.com

                          fret  ___________
                                | | | | | |     once the concept is mastered, 
                        1       |.|.|.|.|.|     options increase by 276 chords. 
                                | | | | | |     (6x4x11)
                                |.|.|.1.|.|
                                | | | | | |
                        3       |.1.|.|.|.1
                                | | | | 1 |     concept:
                                |.|.|.|.2.|       F9, Am7-5, Cm6, A 1/2dim
                                | | | | | |       are really one chord that
                        5       2.|.2.2.|.|       has different uses/names.
                                | | | | | |
                                |.|.|.|.|.|       listed here are 6 common 
                                | | | | | |       voicings.
                        7       |.|.3.|.|.|
                                | | | | | |
                                |.|.|.3.3.3
                                | | | | | | 
                        9       |.|.|.|.|.|
                                | | 4 | 4 | 
                                |.|.5.|.5.|
                                | | | | | 5 
                        11      4.|.|.|.|.|
                                | | | 4 | | 
                                | | | 5 | | 
                        12      |.6.|.6.|.|
                                | | | | | | 
                        13      |.|.6.|.6.|


Well, say your comping on A7...substitute one
of the six variations. Remember when comping,
depending on the style of music, you *can* substitute
9th chords for added color. So for this A7 example (keeping 
it as simple as possible I hope) I would rearrange this to:

                          fret  ___________
                                | | | | | |
                        1       |.|.|.|.|.|
                                | | 4 | 4 |
                        2       |.|.5.|.5.|
                                | | | | | 5
                        3       4.|.|.|.|.|
                                | | | 4 | |
                                | | | 5 | |
                        4       |.6.|.6.|.|
                                | | | | | |
                        5       |.|.6.|.6.|
                                | | | | | |     
                        6       |.|.|.1.|.|
                                | | | | | |
                        7       |.1.|.|.|.1
                                | | | | 1 |   
                        8       |.|.|.|.2.|   
                                | | | | | |   
                        9       2.|.2.2.|.|       
                                | | | | | |
                        10      |.|.|.|.|.|       
                                | | | | | |       
                        11      |.|.3.|.|.|
                                | | | | | |
                        12      |.|.|.3.3.3