Adding a new provider is quite an important change for jclouds. The first thing you'll want to do is review How to Contribute. We need to make sure it will work properly and we'll be able to properly test it so don't be discouraged by the reviews. A good example of a JIRA issue for tracking the development of a new API and providers is Implement OpenStack Marconi and Rackspace Cloud Queues.
Having said this, a number of general considerations to take into account when starting a new API or provider:
New providers are added in labs (labs, aws, openstack) first, until they are stable. For more information on how APIs/providers are considered for promotion out of labs, see How Does an API/Provider Get Out of Labs?
We require both live and mock tests. "mock" tests verify that the api generates the expected request according to the method annotations, and that the response is properly parsed. We use MockWebServer to do that, and you can take a look at the MockTests classes of an existing api.
See the API/Provider Writing Practices for more detailed information on code style and other guidelines.
Which API or provider should you choose to use as an example for your work? It depends! Please email us on our dev@ list to describe the work your doing and we will recommend one. The earlier you get engaged with the jclouds community, the easier the whole process will be.