When a friend of yours loses his or her father, it's important for you to express your condolences simply and honestly without turning the loss into an occasion to talk about yourself. Look for opportunities to provide your friend with a practical service that shows how you care and lifts some of their day-to-day burden. Avoid giving your friend advice, and just allow them to grieve in their own way.
When you express your condolences to your friend, simply tell them that you are so sorry for their loss. If you have pleasant memories of your friend's father, share them, and let your friend know how much their father meant to them. Do not share unhappy stories or commiserate if your friend did not get along with their father; it is considered very poor manners to speak ill of the dead.
Offer to help with providing meals, babysitting needs or funeral plans, if it would help your friend to have some responsibilities removed. Avoid talking about the loss of your own parents or parents of other friends; each person's grief is unique, and it does not help your friend for you to turn the attention on yourself. It is not necessary to say a great deal when expressing your condolences over the loss of a father, but it is necessary to say something and to make it clear to your friend that you are there for whatever they need.