How do you write a terms of service?

This is very dependent upon the exact services you are providing and your particular situation. There is not a "one size fits all" solution for this.

You should have an experienced lawyer write your Terms of Service. The Terms of Service is actually a contract between the website and its users. It is crucial to have a well-written Terms of Service that protects you, spells out dispute resolution, and lets your users know very clearly what is allowed and what is not. I write Terms of Service and can tell you that each website business is significantly different and the Terms of Service must specifically meet the needs of that website business. Once the lawyer writes your site's Terms of Service, she or he will also need to continuously update and tweak the Terms of Service to reflect changes in the business and things you have learned as you go along. A Terms of Service is never final and will be constantly evolving to reflect challenges to it that have been revealed. Do not skimp on spending to have a lawyer write the Terms of Service. It will be a significant legal expense, but a crucial one.

Most "terms of service" are fairly complex, especially if they involve services offered on the Internet. It will be worth your while to hire a knowledgeable contract writer or attorney to help with this matter.