The best time to do a self-exam is when the breasts are not tender or swollen, so avoid "that time of the month." Most experts suggest checking your own breasts once a month but every weekend is better. You need to get to know what's "normal" for your breasts.
All women over 20 years old should examine their breasts whether they are natural, have implants, are pregnant or are nursing. If anything is unusual, make a doctor appointment for the same week. Most of the time, it's nothing to worry about. But if it is cancer, an early find and fast response can make a difference in how far it spread and whether you have to have mastectomy or lumpectomy, and whether you can to go through chemotherapy.
Breast cancer is not restricted to "old people." There is a growing group of women in their 40's getting it. It is also linked to high hormone levels due to the Pill, hormone replacement therapy and pregnancy. Hereditary breast cancer can strike at any age.
In the "old days" it was recommended to do examinations while standing in the shower. Nowadays laying on your back is the recommended way because the breast tissue spreads more evenly across your chest which makes it much easier to feel all the breast tissue.
Use the finger pads of the 3 middle fingers on your left hand to feel for lumps in the right breast. Use the right hand to check out your left breast. Make overlapping circular patterns with your finger pads to feel the breast tissue. Do this once lightly, again with medium pressure, and then a third time with firm pressure so you can feel down to your ribs.
Do the entire "circle" of your breast, in between them (sternum/breast bone) and all the way up to your collar bone. Your breast is actually teardrop shaped and goes up pretty high. Also check your sides up into the arm pit.
While standing in front of a mirror with your hands pressing firmly down on your hips, compare them for changes in size difference or shape. Check the skin for dimpling, redness, scaliness, orange peel textures, dimpling, inverted or changed nipple appearance. Use a hand mirror to examine the undersides.
Examine your underarms while upright and with your arm only slightly raised so you can easily feel in this area. Don't raise your arm too high because this makes the skin and muscle real tight which makes it harder to find changes.
These self exams are very important. I found my lump this way - it was very high toward the collarbone and too high to be captured in mammogram pictures. Mammograms alone are not enough. You must do both.