Search for John Deakin's articles on engine management. You can pull the mixture control at a fair pace, until you feel a slight deceleration. If the engine remains smooth, then you are already LOP and all is well. If it is not smooth, enrich until smooth.
if you do this at 65% or less, you cannot hurt the engine with the mixture control. Carbureted engines are more difficult to run LOP because the fuel/air distribution is less uniform. Some cylinders may be running ROP while others may be LOP. LOP will provide less horsepower than ROP and thus loss of smoothness.
EGT is just a way to navigate the power/mixture curve. Hottest CHT (the temperature that matters most) is found at about 40°F ROP.