Mix at a lower monitoring level! Mixing at lower monitoring levels is one of the keys to great equalibrium / flat frequency response. In my career I've been blessed to have mixed many different styles of music, yet one constant holds true in every genre. If your mix can sound great at a low monitoring level and in mono, then once it's played with properly crossed-over subs and high-end main speakers, then - WOW! It will sound great once it's played in a club or bar. Truly listen to four or five of the greatest mixes you can find, at a low monitoring level and compare it with your finished mix. 99% of the time, a major release will sound just as clear and punchy, at ANY monitoring level.
Test or monitor through car speakers and headphones! Some studios actually have a car in the main studio, just for previewing mixes in the most widely used environment. This technique has been used for decades with car speaker type monitors also, e.g., Yamaha NS-10's. The NS-10 monitor is a car speaker mounted into a box and used as a near-field studio monitor system. Cars and headphones are the main mediums used by consumers, for listening to music and our mixes. So, why not monitor and listen to your mixes (before the world hears them) through the same type of system? Well,... it's a proven fact that, a mix will mirror how it sounds in a near-field system or head phones, as it will once played loudly in larger, more expensive systems. And, in my humble opinion, the NS-10 is a terrible sounding, over priced speaker! Yet, they're a mainstay within the major recording studio market. I can't remember going into a major recording facility and not seeing a set of NS-10's sitting on the desk or console.
Use VU meters in conjunction with dBFS meters! I use Coleman VU Meters in conduction with my dBFS meters, throughout the tracking, mixing and mastering process. dBFS meters are mainly used (when calibrated properly) as a visual indicator of the maximum before clipping or distortion level. When I want to see my true, low-end and RMS response; I use my VU meters! Also, whenever I solo a channel I'm mainly looking at the VU meters for the bounce of the signal and the , which usually relates to any release settings of compressors in my gain structure.