Watch the Dominant Chords online guitar lesson by Jeff McErlain from Blues Survival Guide: Rhythm Edition
I don't know about you but the first time I saw the symbol A7b9b13 I just about fainted. Actually I think I just played A7 instead. How about "The Hendrix Chord" otherwise known as E7#9? Dominant 7th chords can handle lots of harmonic information. Meaning, you can really have fun with them by adding in upper structure triads above the chord tones. For example G7 is spelled G, B, D, F . If we were to fill in the missing notes of the scale we would get A, C, and E. These notes are the 2nd, 4th, and 6th. If we were to bring them up an octave they become 9, 11, and 13. These are what are called natural tensions because they occur naturally in that key. Altered tensions are when we alter or change those natural notes. Such as b9, #9, b5, and b13. It is essential you become used to these voicings and the easiest way I believe is to study the attached pdf. This way you can see them as shapes at first to get rolling. This can take you a long way, and stop you from passing out on a gig when you see one of these mysterious "jazz" chords.