Gather as much info as possible on their requirements. Refer them elsewhere unless they are enterprise class and a good fit. Send price quote fairly early usually to qualify the prospect. Create a free trial account. Share API documentation page. Schedule biz and dev calls as needed. Usually do some sort of pilot with larger prospects. Set up sandbox accounts and API access for dev and testing (which we require of API integration partners). Review and negotiate contract (we have a simple two page agreement and order attachment, but sometimes have to do the deal on their paper).