Apple built a terrific page on its website with a variety of short videos showing how to take better photos with iPhone 7. Each of the 16 videos focuses on one brief lesson, demonstrating a photography tip in 3-5 steps.
The videos are produced well, fun, and above all practical. I think there is at least one technique everyone with an iPhone will benefit from in these videos.
Many of the videos illustrate the use of exposure control, which is a technique I think many people don't know about on iPhone. It is easily one of the best things for anyone to learn to make their photos better, and these videos explain the benefits very well.
My favorites of the videos are How to shoot without flash and How to shoot with street light. They both show how a great photo can be taken in low light without using the obnoxious flash.
Check out the videos and then put them into practice. If you shoot something you are especially proud of, let me know on Twitter.