What should I look out for on a day to day basis to ensure that I don't develop breast cancer?

No good answers. No one knows for sure what lifestyle activities decrease a woman's risk of breast cancer. But regular exercise and avoiding alcohol seem to help. Regular exercise means doing about 30 minutes a day, 5 days a week of moderate-intensity activity like brisk walking, running, cycling, swimming, or dancing.
Early Diagnosis"key" I agree with drs. Greenhut and harris with respect to the benefit of a healthy lifestyle and performing self-examination. The only point i would add is the importance and underutilization of mammography. All women should begin getting mammograms at age 40, and yearly thereafter. Diagnosing breast cancer before it becomes palpable leads to the highest cure rates.
Nothing daily. There are subtle changes that occur in the breasts with breast cancer. Checking daily will not help pick these up. Examining your breast monthly about the same time in your cycle is the best way to find changes in your breasts that may be significant. I usually tell patients that "lumpy oatmeal" feeling is normal, but peas and marbles aren't.