It is not unlikely that you just need to persevere with the lens and shoot in a range of lighting conditions ect before looking at adjustments. I have known a good number of folk who have purchased their bazookas, put them on the camera and captured a whole heap of crap images.
Everything is working against the photographer at long focal lengths, and bear in mind that wishy washy light is quite likely to influence the images in the same manner. Recently a friend of mine bought the Canon 100-400 and 1.4 Extender and subsequently sent me a load of images he'd taken which he thought were OK, personally I'd have formatted the card before anyone else got near them. I thought he'd taken them using a smart phone with some additional clip on lens attached.
I checked out the kit for him and found it was fine. His problem was unrealistic expectations in poor light and not realising that a small tit is still a small tit regardless of how much glass is attached to the camera. He'd looked at some really tasty images, bought the kit and thought the kit and proceeded to shoot anything which moved and a heap of stuff that didn't. It does take a lot of shooting to get really good with a long lens and in the meantime really good conditions will likely deliver some decent frames to keep one sane.
Not to say categorically no tinkering will be required, more a case of rule a out the other stuff like all the matter that's in the air across a long distance, poor light and insufficient shutter speed/aperture optimisation. And keep it all as still as possible.