For bass I'd say this :
try to see where the kick's dominant frequency is (generally 60 - 80 Hz), use filters or EQ to make room for the kick drum here. It depends on what you want to achieve balance-wise.
Then I watch the low mids : 100 to 800 Hz area is crucial because a lots of instruments fight there (guitars, snare, vocals...), you have to make room for everyone without killing your tones. Maybe a dip around 250-600 can help to get the bass in the mix.
Watch also the 100-200 Hz area : bass rumble here, that's what makes your tone full. Solo the kick and bass to see how it's fighting, this area can kill you, it can sound very thin or too "busy", you have to find the good balance.
800-1 k : this range can help you to make the bass more present, try a slight boost here (bit of distorsion should help to get the "growl" underneath the guitars, espacially in a rock/metal context).
1k - 3000 Hz : Presence. Reduce or boost, depending on how it was tracked and how it sits in your mix.
Do not be afraid of compression ! Try different things but basses in mixes tend to be very compressed, or even limited. Any kind of dirt can be cool too