Justify the cost
The Apple products are well made and are really good to use. The problem (for Apple) is that these good products last a long time and Apple really doesn't give you a compelling reason to upgrade. They are expensive too meaning that it has to be worth the money to upgrade the device. Most of the new models over the last few years really did not offer anything revolutionary to justify an upgrade, so people hung on to their current phones.
The display on my iPad Pro is the same that was on my iPad Air. But the reason i upgraded was after 2 years there were a number of features that could justify the upgrade-plus i was able to sell my old device which reduced the cost of the new one.
Cameras are nice but not revolutionary. Processors are nice but don't really make a noticable difference on a lot of regular apps.
The Apple Watch really could use improvement. The third party apps are very slow to update for the most part, the faces are boring and the device is pretty sluggish. I'm not really sure what the new watches offer as the Apple website did not really go into detail as to the improvements. All they seemed to focus on were the new bands. So i will probably hang on another year to my current watch.