I found a16z's blogpost of basic metrics great for starters--

https://a16z.com/2015/08/21/16-metrics/ https://a16z.com/2015/09/23/16-more-metrics/

Note on 16 metrics #7-- from what I understand bookings actually don't increase A/R until the services are rendered, so know what you're looking at if you don't get cash up front.