The best ways to express sympathy or offer condolences are to send flowers, write a card, visit the person concerned or make a donation to an appropriate charity. It is important to consider your relationship with the people affected and decide what is most appropriate.
When writing a card, it can be difficult to decide what to write, especially when someone has died. Remember that people are often comforted by the knowledge that they are not alone in their time of sorrow. Consider the situation. Is it a work colleague? If so, you may wish to send a card and flowers expressing your respect for the individual. Explain how much she is missed. Perhaps it is a next door neighbour. In this situation, you may choose to offer a home-cooked dish or help out with various tasks.
There are some words to avoid, so it is important to consider what not to say. Make your message about the person bereaved and not your own feelings. Things to avoid include: "I know how you are feeling" or "I don't know what I would do in your situation." Most importantly, don't pretend it hasn't happened. It can be tempting to avoid the person because you are afraid of upsetting them. Whatever you say, make sure it comes from the heart.