You can reduce your API usage by allowing your developer console session to "idle". Once idle, you'll only incur one API call per incident (such as saving a class, running a test). While not idle, the current implementation polls the server once every 6 seconds, or 10 API calls per minute while doing absolutely nothing.
Also, using the Force.com IDE will drastically reduce your API calls, because you won't suffer from the "monitoring" API calls. Believe it, it makes a big difference.
For those interested, I asked this myself on the Salesforce Community:
@Josh Kaplan (Salesforce.com), in addition to the code coverage
glitches in the API, your comment
retiring the setup pages in exchange for the Developer Console is
worrisome. Today, using the console consumes one API call per six
seconds per developer. Given that a normal developer org has 5,000
calls per day, this means that two developers working in the same
organization (the maximum a normal developer edition supports) can
only work for 4 hours a day actively in that organization before
exhausting their daily usage limits. If we are required to use the
console, we will be limited to working just a few hours a day inside
the platform. Is there any plan to have the console no longer use API
Josh Kaplan (SFDC PM) had this to say:
Starting with the coming release the number of API calls will
dramatically decline. Results will be streamed, so polling will not
consume so many API calls.
Presumably this applies to Spring '14.