Follow The steps -:
1) Force Stop Running apps and Remove Some Apps which started Automatically
2) Remove some Widgets Which you Are Using On The Home screen
3) Don't Use High Quality Image as Wallpaper, Why? Because Sometimes That Wallpaper Makes Your Phone More Slow.
4) Root Your Phone And Uninstall Some waste System app (Please Know The All Features of System app Then uninstall Because If You Remove any Wrong App You May Face Problems)
5) Remove Transition Effects-:
Open your Phone Setting and go to About Phone
Tap on build Number 5 Times to enable developer option
Now Go back and go to developer option and switch on the setting and search for Windows transition scale and change the value to 0.0 Means Off It
6) Always Update Your System if Any New Update Come , Because This updates Fix Many Bugs