There is no clear answer to this problem, because the problem is caused by the specific frequencies that the other band members' instruments (*cough* guitar *cough*) occupy which compete with your bass guitar, and the specific frequency response that your particular combination of equipment will produce (and can be exacerbated by the room in which you are playing, etc.).
Listen to a recorded song in which you can clearly hear the bass. Typically there has been sonic "space" carved out of the mix in order to facilitate this; consider that this space is typically created by EQ cuts applied to other instruments, so that the bass can be heard clearly.
In a live performance situation, band members are practically never this aware of the problem and how it affects the other members, and/or are rarely so altruistic that they are willing to do this for each other. I single out guitar players in particular because they usually believe (and, often, rightly so) that, BY THEMSELF, they sound "best" with a full sound that occupies as much of the frequency spectrum as possible. While this may be true, in a band situation they are obviously no longer playing "by themself" and would make the entire band sound better with a few judicious EQ cuts. A good soundman will do this at FOH ("Man, that guy always makes us sound amazing!") because it's a common problem, but it usually doesn't solve the problem on-stage.
So. If you can't get the other members of the band to turn down their low-mid and lower bass frequencies ("Hey y'all, I got that covered!") then what you need to do is to find "the hole." That is, find one of the specific and likely narrow ranges, probably most palatably somewhere in the low-to-center midrange (and perhaps also at the very bottom), to boost in the frequency spectrum so that you can be heard. This will be a gap of sorts in the frequency spectrum that is least occupied by others. Finding it can be more easily done with a frequency-sweepable equalizer (i.e. para- or semi-parametric eq) so that you can boost a frequency and "sweep" it in order to find the right frequency to boost so that you can be heard. Often, once you find that magic frequency, you won't have to find it again if you continue to play with the same group of musicians.
That's how I do it, and I also suspect that this is how a lot of classic midrange-y bass tones have been born over the decades.
