Amy, I recommend you go and ask your GP to show you. It is very important to do it every month and to do it correctly. This is a pet topic of mine as mum has had breast cancer and I have had a precancerous lump removed already (about a year before conceiving DS1).

The best time of the month is early in your cycle, a few days after AF starts, as this is when they are less lumpy. Lift one arm above your head, and with your other hand gently start under your arm and work your way around the whole breast. You are feeling for any changes or lumps (a lump might feel like a pea under the skin, or just like a lump. If you are not sure if something is a lump or not, go and get it checked. It is better to be on the safe side.

Good on you for asking this question. As well as helping yourself, you might be helping someone else who doesn't know too!