Approaching the rest of the mix after solidifying the rhythm section is very much the same in terms of the 5-step process. Levels, pans, EQ, compression and FX/details.
Using the drums as your reference level, begin bringing the levels up of each individual track starting with the bass. Mixing the low end of the spectrum is arguably the most difficult yet rewarding part of the frequency spectrum. Once the low end is levelled and balanced properly, the rest of the mix process becomes far more effective.
Deciding on dominant instruments is important here. Not everything can be front and centre, and heard at the same time. Choose a few elements and focus your mix around this. If decisions become difficult at what should be the focal point of a mix, extra articulation is likely needed to have things move in and out of the main focus via stereo panning, effects and automation which is tackled later in the process.
Low frequency information needs to be pushed further for our ears to perceive but low frequency in abundance will diminish head-room fast. That being said, there is a fine balance between too much and too little low frequency information. It becomes important to understand the perception of the human ear in terms of frequencies. The ear is highly sensitive to frequencies between 2kHz and 7kHz, thus, this band doesn’t need to be pushed as hard. Refer to the equal loudness contour and make note of where our ears are sensitive and where they are not.
Sub basses should be worked together with low bass instruments. The sub bass, low bass, low-mid bass, the kick, and other heavy drums all occupy the same frequency bands so they must all communicate with one another and share the space. That goes with the rest of the spectrum too, except, higher frequencies are in an abundance and due to their audible characteristics can share more of the space and be moved around the stereo field.