There are some ways the official Inform documentation is great, especially the quantity, variety, and depth of its examples. I don’t think providing an easy on-ramp for beginners to the language is one of the things it’s good at.
But I think Creating Interactive Fiction with Inform 7 does a very solid job at both teaching Inform 7 and fundamental game design issues.
(If you haven’t already, check the list of Inform 7 documentation for pointers to resources labeled by what version they were for. And there are a couple of very good, recent free tutorials to tide you over while waiting for Creating Interactive Fiction to arrive if you end up ordering a physical book…)