On the power side - if you are using 120V at the rack consider increasing the voltage to 208V  it is usually availble at the power distribution panel and it can improve energy efficieny by  3-5%. This can usually be accomplished by utilizing the exsiting cabling but chaning out the outlets at the racks and the breaker at the panel (Check with your local electraican to meet national and local codes)

On the cooling side, consider optimizing airflow to avoid mixing hot  and cold air. Blanking panels are by far the simplest, cost-effective, and most misunderstood item that can improve cooling efficiency. By ensuring that the warm air from the rear of the rack cannot flow back into the front of the rack via open rack spaces, blanking panels immediately improve the efficiency of the cooling system.

Look at raising temperature,  It has always be the "rule" to use 68° to 70° F as a set point to maintaining the "correct" temperature in a data center. While each manufacturer is different, most servers will operate fine at 75° F at the intake. so long as there is adequate airflow.  (ASHRAE 9.9 now specifies up to 80F at the air intake to the equipment)

Most CRACs maintain humidity by adding moisture and reheating the air. The typical target set point is 50 percent humidity, with the high-low values at 60 and 40 percent. Simply changing set points to 75-25 percent will save substantial energy.

In many installations each CRAC is not in communication with any other CRAC. Each unit simply bases it temperature and humidity setting on the temperature and humidity being sensed in the (warm) return air. Therefore it is possible, and even common, for one CRAC to be trying to cool or humidify the air while another CRAC is trying to de-humidify and or re-heat the air. The cooling system contractor can add a master control system or at least change the set points of the units to avoid or minimize the conflict.

Consider adding economizers to the cooling system if feasble. In cool climates they can pay for them themselves by providing  "free cooling" when the outside temps fall below 50F. Over time this can cut the cooling energy by 20-40%, depending on the climate.