Uh oh...we've gone there.
Speaking as both a bassist and a guitarist, I can relate to the sound challenges faced by the players of both instruments.
Electric guitar is loud in its immediate proximity and tends to be very directional - ie: the speaker cab throws the sound out about 20 - 50 feet in a beam. Step out of the beam and it is almost inaudible compared to the bass & drums.
Electric bass is not as loud in its immediate proximity but is much louder in the room (and beyond).
Drums are another issue altogether - they have no volume knob and most drummers that I've played with are quick to point out the harder I hit, the better the tone. So that usually sets the bar for everyone else.
At the risk of being overly simplistic, there is little or nothing that can be done to compensate for any of this as it is directly related to size of the sound waves produced by each instrument.
So, the most important thing you can do (besides controlling your volume) is to aim your speaker cab / monitor up at you and step away from it. If your cab is aimed at your feet and you are standing right next to it, you will perceive less high end and, since the sound is blowing right by you, less volume. This will make you want to compensate for both and it's game on.
Also, it is deadly to set up facing each other as your sound is gonna be killing someone and vice versa. If you must set up facing each other, a better thing to do would be to stand near another person's amp so yours is facing you.
Along those lines, an interesting thing to do if you have a wireless is to set up as you normally would for your gig and dial in what you think are ideal tone & volume settings for the situation and then walk around the room while playing during a sound check. You'll be amazed at the change in the way you perceive your golden tone.
And - when the audience shows up, that's another variable in play. People are like giant pillows, they absorb high end. as such, you may need to recalibrate slightly at the end of the first set to compensate.
One last thing - I believe it was Miles Davis who said If you can hear yourself, you're too loud.