When mixing your mid-range, try using some saturation on the mids using frequency-specific saturation - additionally, utilize upward compression to that same range. If your mix can benefit some aggressive mids, try an aggressive bus that isolates the mids, compresses, distorts, and upward compresses.
In my opinion, the best way to add a lot of power to your mid-range is to use frequency-specific saturation to create harmonics that make your fundamentals more easily perceived. This distortion will make the range sound full and impressive by amplifying in-key aspects of the range.
I like using FabFilter’s Saturn 2 for this, but Trash 2 by Izotope is another good frequency-specific saturation plugin.
Using the FabFilter multiband, I can create upward compression by combining the compression setting with a positive range. This means that the quieter aspects of the range being compressed will be captured and amplified from the bottom up - in this case, the mid-range of an instrument or bus.
Low-level compression creates a very full sound so use it when the mids sound weak.
If the mid-range of a mixbus, stem, or instrument is sounding too separate or like it needs to be blended a bit, use very subtle high-density reverb on your Mids. The higher number of reflections caused by a high-density setting ties everything together.
Again, use this at a lower setting if using it on a stem or mixbus, but it can be used more aggressively on an individual instrument.
If you need to control your mid-range’s dynamics, set up a parallel track using a bus or auxiliary send - first insert an EQ with a high and low-pass filter, then insert a compressor. Use a quick attack and a medium release, about 100 to 200ms will work well.
This way you can compress the mid-range and significantly control it, then blend that compression back in with the original signal.
Following the last concept, use the same EQ settings on the auxiliary send, but then introduce aggressive stylistic compression. After that, use a saturator with moderate settings, and lastly use a low-level compressor - this will isolate the midrange, distort the mid-range, and then increase the detail.
This can sound really intense so use this if you want a really aggressive mid-range.
If your mid-range is sounding boomy, or disharmonious in some way, find out the key of your song and then reference the notes that are being played. For example, if your song is in the key of A major, a C shouldn’t be too prevalent.
In this case, find the frequency that corresponds to C and attenuate it. Cut these disharmonious notes from the mid-range, but only by 3 to 6dB - no need to do it aggressively.
On your mixbus, so when affecting the full mix use a multiband dynamics processor and use upward expansion on the mid-range. Use a quicker attack and then try to time the release with the BPM of the track to give it a bouncy, musical feel.
I’d recommend doing this only by a couple of dB, and ensure that the threshold isn’t being triggered too often.
The upper edge of the mid-range may need some attention too since it’s where you have the majority of your vocal and clarifying instrumentation. Use a high mid-band or an exciter to add some clarity and detail to this section - fresh air by slate is a good option.
Also, Izotope’s exciter can be made frequency-specific, making it great for adding clarity to the high mids.
Using a mid-side equalizer, expand the width of the mids by amplifying a sideband, or increase the power of the center by using a mid-band. I find that slightly boosting the side’s low mids in an instrument bus can make the entire mix sound full.
Additionally, using this method to pull out details that are being masked, in turn adding more detail to the mix.