I like this, taken from the BHA:
Live your life based on humanity and reason and recognise that moral values are properly founded on human nature and experience alone. Base decisions on the available evidence and an assessment of the outcomes, not on any dogma or sacred text. Atheism and agnosticism is an active and ethical philosophy far greater than any negative responses to religion. Foster individual rights and freedoms but believe that individual responsibility, social cooperation and mutual respect are just as important. People can and will continue to find solutions to the world's problems so that the quality of life can be improved for everyone. Be positive, gaining inspiration from life, art and culture, and a rich natural world. We have only one life and it is our responsibility to make it a good one and to live it to the full.