Many women can express some fluid from their nipples on squeezing. This is a normal response and is the way in which breast feeding works. Persistent squeezing of the nipple will tend to encourage the discharge to continue, so we would advise you not to do this.
If you have a nipple discharge that is blood-stained, comes out by itself or is very profuse you should report it to your GP. Even in this case most discharge is not related to breast cancer but to benign changes, but it is important to have it checked to make sure.