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Very generally, the basic measurements that will prove most useful will be the impulse response, from which can be derived both the frequency response, cumulative spectral decay and the Envelope Time Curve.
The frequency response can also be measured as a time averaged measurement by playing pink noise over a period of time, and any transient/spurious noise sources will be 'averaged out'. You may find this method advantageous for LF room mode measurements as it will insure the proper pressurization of the room over the low frequencies. The waterfall display perspective is also available.
You will find the frequency response and waterfall below about 250-300 Hz useful for identifying room modes. And as the region where modal behavior ceases to dominate, the ETC will show you the gain and arrival times of specular reflections.
While many focus solely on eliminating first order reflections, the ETC allows you more granular information and control.
It can be used to identify and address such fine issues as cabinet diffraction, driver signal alignment and speaker positioning issues to first and higher order reflections as well as the energy content of each (a factor that is easily as important as simply the arrival time!). From the information provided, the precise paths of the various reflections can be determined and subsequently treated as appropriate for their arrival time, gain and temporal and spatial distribution.
From these measurements, and according to your desired acoustic room response model, the geometry of your room, your creativity and budget, you can then use the responses to guide your application of the various treatment tools as you manipulate the total energy response of the room via absorption, reflection, and diffusion such that you accomplish the tailored response you desire while 'seeing' exactly what is occurring spatially and temporally in the room before and with each step of the treatment.
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