Given the quality of the inflight you've posted here, I'd say you need little advice as it's a cracking shot. Not so much technique related but I think it does have a little too much space and would stand some cropping. That's by the by though and subjective.
Inflights have never been my forte, not yet but I'm working on it. A couple of weeks ago, I was on the Isle of May with the seabirds and puffins were flying about like little bombs. It took me a while to hit my mark but once I did, I got a hit rate of about 50%. It was of course much easier with hundreds of puffins flying around on similar flightpaths, rather than a single, potentially sporadic kingfisher. For that I had my 5D in AI Focus and Tracking Case 1. I found even the 5D struggled with messy backgrounds but it tracked with ease against the sky/sea, with a 150-600C. Nailing focus is first priority but is challenging, good light and higher shutter speeds help, I more often that not have the aperture as wide as the lens will allow at a given focal length, in my case for example, f6.3 at 600mm.