Although it is normal that our Android go fluid (or fairly fluid), there are times that this slows down greatly.
To fix this we must first know the probable cause: lack of RAM. For those who do not know what it is, RAM is a type of memory used to store data applications that have open, so if we have many applications running on our device this will slow down, because this memory you will be full and you can not charge more.
To avoid this we can try to close all applications we have in the multitasking, which can help. In addition, we could also find applications that are always running and close and / or uninstall them.
An application we may find very interesting for all this would Greenify. This application will allow us to prevent applications that do not want to stay in the background, closing them once we get out of this. In this way we avoid that their processes are loaded into RAM and slow down your phone.