Harmonics

I'm starting to hear harmonics / overtones a lot more now when I play guitar and bass.I understand that EQ can manipulate the overtones so the instruments sit better - I was wondering if anyone had any specific guidelines when EQing guitar and bass ? I guess at certain points the guitar and bass will share the same frequencies  -but  which overtones should I cut that will make a differance to the clarity of the two instruments ? At the minute I'm trying to hear the overtones and then decide wheter to keep them or not !! Are some overtones more important to the sound than others ? I can hear the 3rd harmonic really well now on both the guitar and bass.I find that if I cut one,and boost the other the two instruments sit better.I find it difficult to hear the 5th overtones,but should the same principle apply ? Does it matter if say both the guitar and bass have a lot of energy around the 5 th harmonic of the bass  (In A it would be around 264 Hz) Will cutting from the guitar to leave room for the bass's 5 harmonic give the bass more colour ? How about the 7 th and 9 th harmonics ?
Great if you anyone can help out on this for me,or give some pointers !
Kev