Those tips are VERY old and outdated, and the author has no idea how iPhones/iOS works. A good example is closing unused apps: When you close an unused app by double clicking the home button this will force close the app. The reason NOT to do this is because whenever you open that app again the phone has to reload everything. This causes more load on the CPU/Battery having to load everything from scratch all over again. If you just use the phone as designed and close the app by touching the home button once to return to the home screen this is much better. The reason being the phone won't close the app, instead it suspends the app in the last used state. The App is NOT RUNNING IN THE BACKGROUND, people think since they don't force close the app that it's running in the background using the CPU, RAM, RADIO, ETC. This is not the case at all, the app is suspended using no resources.
Next disabling LTE is another bad idea, years ago when LTE first came out and coverage didn't exist everywhere then yes disabling LTE helped since the phone would turn the off LTE radio. However now that LTE is widely deployed everywhere keeping LTE ON is better, for two reasons: LTE is faster, so the phone gets the data faster and the CPU enter a rest state sooner. Next the LTE interface is more modern/efficient than GSM/HSPA/Circuit Switched interface, and you will get batter battery life using LTE than older circuit switched interfaces.
Disabling Auto brightness also isn't a great idea, it's better to use Auto Brightness and have the phone DIM the screen in dark ambient lighting, and raising it automatically in bright ambient lighting/outdoors. This is better than having to manually adjust brightness, because of human error you can forget to lower the brightness causing battery drain.
Once again I suggest you leave network selection on AUTO. The phone/operating system is smart enough to choose the correct network under all conditions. I would also reset network settings after to ensure you're running the optimal settings.