There are two basic activities: looking and touching:
Stand naked in front of the mirror and look at the shape of your breasts. Get a sense of how they project. Lift your arms, put them on your hips and bend forwards. Be aware of any changes in shape or the colour of the skin.
Feel your breasts. Run your hand over the whole area so you’ll get to know them. This is easily done when taking a shower with soapy hands or when you use body lotion. Lumpiness is a normal feature of the breasts, as you will notice. What you are looking for are lumps or swellings.
Do the same lying down. Place a folded towel under your right shoulder and lift your right arm over your head, so the breast tissue lies over your chest. Feel your right breast with your left hand. Repeat the procedure for your other breast.