4. Clean up reverbs and delays as well
Considering space treatment as just common audio effect is quite wrong. At mixing sending sounds to AUX channels (e.g. reverbs and delays) engineer introduces another extra instruments which require for individual space in a record without loss of audio transparency and overall music clarity. It all ads up to that this elements equalization might be needed as well. In fact it means you'll have to make their complete rap mixing and mastering services. Since even being added at considerably low volume level they still require for space in recording already busy with other sounds. So the starting point of their elaboration is very alike common instruments and/or sounds mixing and mastering. Firstly reverberation should be filtered of the very sub low frequencies - there is no any legibility, just a muffled mumbling obscuring Bass and Kick. For more clarity you better High Cut delays - of course if you're not aiming for specific effect with clearly audible echoes. This simple approach is straightforward way for engineer to right away put the delay further back in music. Thus delays perfectly does it's job of imparting music better feeling of space.
In busy music tracks isn't easy sometimes to recognize which exactly frequencies clogging up entire sound of the record. In this case most of audio mixing engineers are making such a trick. They crank up delays and reverbs AUX channels so that their presence in the song got more obvious. Now it's quite easy to define audio muddiness sources and chunk them out with an EQ. What's important - experienced engineers are taking care of clarity of the audio even before equalization. Just with setting up right-minded reverberation decay time and delay's feedback. A short pre-delay on reverberation plugin will also make further professional mixing and mastering more simple and help to separate sounds from each other.