If you have not been exposed to the fiasco that occurred before, but your iPhone is still slow, we will tell you in a few simple ways. You must already know the fiasco. As you know, Apple was deliberately slowing down the experienced models. Even the battery replacement campaign for apology was made last year.

Back up your photos to the internet. Google Photos is a unique app where you can do this. In this way, your phone will breathe easily as you will save space.
Always uninstall the applications you are not using. No need to stop it on your phone. Save on the ground and prevent it from running in the background.
Old messages will use your phone to destroy and keep busy. Back up and delete if you want.
Clean the safari. If Safari accelerates, your phone will also be accelerated. Settings - delete history from safari section.
Turn off automatic updates. In this way, you can prevent it from running in the background. Your phone will not be busy with it.
Automatic download If there is an application you downloaded for iPad, it will download it to iPhone device simultaneously. Turn this feature off.
Don't let the application open in the background. If you have not released the tape, turn them off one by one.
If you do not have wifi access, you must switch it off because it constantly searches for the network. It eats cooked and keeps the phone busy. If it is already connected, there is no problem.
Turn off your phone every few days and wait 5 minutes. This will make him refresh. It caches the cache.
Make sure to update when it's time. But don't do it right away when the new version of iOS is released. Wait for it to be stable. Make sure to do it later. Because applications will become more stable.