These are pretty applicable to theists in addition to atheists.
- Do not feel absolutely certain of anything.
- Do not think it worthwhile to produce belief by concealing evidence, for the evidence is sure to come to light.
- Never try to discourage thinking, for you are sure to succeed.
- When you meet with opposition, even if it is from your family, endeavor to overcome it with argument and not by authority, for a victory dependent upon authority is unreal and illusory.
- Have no respect for the authority of others, for there are always contrary authorities to be found.
- Do not use power to suppress opinions you think pernicious, for if you do, the opinions will suppress you.
- Do not fear to be eccentric in opinion, for every opinion now accepted was once eccentric.
- Find more pleasure in intelligent dissent than in passive agreement, for if you value intelligence as you should, the former implies a deeper agreement than the latter.
- Be scrupulously truthful even if the truth is inconvenient, for it is more inconvenient when you try to conceal it.
- Do not feel envious of the happiness of those who live in a fool’s paradise, for only a fool will think that is happiness.
And then there is this single commandment for atheists. Which I have a hard time following.