Consider the following if you have a low 260/280 ratio:
The correct amount of DNAzol reagent may not have been used. If DNAzol reagent was added to a cell pellet, make sure that the volume of reagent is 20 times that of the cell pellet.
There may have been a problem in pipetting away the viscous supernatant from the DNA pellet, leading to contamination with protein. The DNA may be used with DNAzol reagent again or extracted with phenol to remove the protein.
In some samples dissolved in water, the ratio may be low due to the acidity of the water or the low ion content in the water. The ratios may go up if the sample is dissolved in TE and the spec is zeroed with TE (or 1 to 3 mM Na2PO4, pH ~8.0). [See BioTechniques 22:474-6, 478-81 (1997).]. The molar extinction coefficient of the nucleotides is given at neutral pH, suggesting that the absorbance at 260 nm would be highest at neutral pH. Of course, DNA is not stable under acidic conditions so degradation may occur if the DNA is left in this condition for too long.