Antibodies, like most proteins, do not like to be freeze-thawed. Avoid repetitive freezing of your solution. The best way to store your antibody is to keep a high protein concentration (>1 mg/ml), add some protease inhibitors, and aliquot it for use. Then freeze the aliquots and keep just one around for day to day use at four degrees C.
Raw serum containing antibodies:
Aliquot into reasonable aliquots (usually 10-50 ml) appropriate to your use of the antibody and freeze aliquots; most serum can be stored safely for months at four degrees with little loss of activity. Due to the presence of protease inhibitors in serum little proteolysis is observed and high protein concentrations keep the antibody in a favorable environment with little denaturation.
Once purified, if the antibody is at less than 0.1 mg/ml add a small amount of detergent or protein (0.1% TWEEN-20 or 1% bovine serum albumin) and some protease inhibitors to the solution to protect the antibody. These should be stored in smaller aliquots (about 1 ml) and frozen for long term storage though the protected solution is also stable for months at four degrees.
This is a bit more problematic as it may contain proteases, purify the antibody of interest if possible. Otherwise just freeze 100 uL aliquots and use as needed by thawing when needed. Don't refreeze.