If you have a single collection focus, it may be sufficient to have a small group of people (known in the current business environment as "stakeholders") who decide in the beginning what kind of terms will go in each field, and one person to add new terms to the Lexicon over time.

In a larger institution with multiple departments, you may need a representative of each department to help make initial decisions about what terms are used in which field. After that, people can submit candidate terms through the New Lexicon Term window, and a central person or people can have responsibility for organizing the terms into the Lexicon.

Sometimes different departments use different fields, or at least different authorities, in which case each department might be able to make their own decisions about the authority to use, and provide a person responsible for maintenance of their section of the Lexicon.

Sometimes people disagree on the authority to be used or on the addition of new terms, so you will need a procedure for resolving these problems. See What happens when curators/catalogers disagree?