Getting started should cover everything developers will need to get up and running with an API. After finishing your API, and you think it is ready for prime time, grab someone who knows nothing about the API, and watch them try to use it. Use what you learn to craft a simple opening paragraph, then some steps users can follow.
Here are some some sample steps to get started.
You should close up your getting started steps with some other helpful information. Depending on the other building blocks you offer as part of API operations, you can provide links to other existing resources.
Make sure and let your users know that you are there if they need help, and to contact you with questions, or if there is anything that can done to make it easier--always be improving on the getting started process.