take this lightly, but it works for me........
usually a kick drum, the bass guitar, and the snare drum are most of the time panned in the center of the audio field. So.......what ill usually do id roll of around 80 hz of the bass guitar to allow the kick drumm to 'thump a bit more. Then ill notch out around 250-300hz of the bass guitar too to allow the kick drum have some "body/meat".
after that...ill listen to where most of the "smack" of the snare drum is.....and ill sometimes notch out around 900-1k of the bass guitar to allow the snare to come through.
listen to these 3 instruments, and find thier best points/frequencies.....and notch aruond trying to emphisize them a bit more so not one instrument will step on its best points