There are many techniques to leaning, and once mastered will result in significant fuel savings. On my CPL cross country, followed by 3 colleagues on the same route - I cruised at FL060-070 using the Piper POH method, and managed the entire route without refueling. They all needed fuel at stop two.
The 'operators' method at the time was to use the EGT guage, as mentioned above - lean until peak EGT is reached, then rich the mix again to achieve a reduction in EGT of 1 division on the guage (i dont remember what the divisions are!)
The POH for the aircraft, and the Piper method of leaning (a PA28) for best economy was to push the throttle to max (firewall) and set the RPM using the mixture. This sounds a litttle crazy, but the proof was there! The economy was great.
Dig into your aircraft POH, it will include the details you are looking for