Applying covering film is one of my weakest skills. That diagram is great because it shows the general rules but we learn as we go.
A heat gun is indispensable especially when covering compound curves like wingtips. One of the biggest discoveries I made was that covering film can stretch as well as shrink. A heat gun makes stretching the film over wingtips much easier than doing it with an iron. I put a work glove on my left hand and the heat gun set on medium-low in my right hand. Leave lots of film to overhang so you can grab it. Heat and pull until the wrinkles you are working on disappear. If there's a wrinkle that won't go away by shrinking with the iron, use the heat gun and stretch out the wrinkle. Lastly, don't trim the overhang of the film until after all the wrinkles have been shrunk out or pulled out.
I had all but one panel on the SE5A wings covered. They looked okay, a few wrinkles. As good as I've ever done. On the last top wing panel I used the iron to tack down and switched to the heat gun to shrink and stretch. It came out so much better I stripped off all the previously covered panels and did them over. Eureka!