Zotero has many citation styles built into the program, however as so many are available if you are looking for a specific on you should search the Style Repository.
For example, here you will find a "Bluebook Law Review" style that may be preferred to the standards included by default. Hovering over the active title of the style will reveal a demonstration of the style. To install simply click on the Install link following the title of the style. You will then see this added to your style options when using Zotero.
Alternatively you can check to see what styles have been installed, and add more by viewing your Preference menu, then selecting Styles.
Since Zotero is an Open Source product there are many people involved in the development process. As such styles are being created, improved, and tested by many people. Below are some steps you can take if you notice issues or would like to request a new style be generated. For expert users who want to delve into altering the code themselves, please continue to the Editing Styles box for more information.
If you would like to request a new style please carefully read through the Style Request instructions.
If you notice errors in a style you are using please follow these steps.
For those who are a tad more adventuresome please utilize the following resources if you wish to attempt and improve upon a style (or even just make local changes for your own personal preferences).
"All citation styles shipped with Zotero, and available in the Zotero Style Repository, are written in the Citation Style Language (CSL). CSL is a new XML-based open standard for configuring citation formatting, designed to be independent of any particular application, document format, or programming language."
Zotero has developed two great resources for those seeking more information on how to create or change their own style.
You may also want to check out the Developers section at Zotero.