Make sure to not have too many processes open at the same time as this makes devices slower.
Because there are many different devices and many types of android OS, they can vary in ways to close background processes.

We are listing the main one, however, if this does not apply to your device, please make sure to use a search engine to find out more specifically.

1. Launch the recent applications menu.
This can be done by pressing and holding the home button on Samsung devices.
Tapping the home button twice in HTC devices.
2. Once the menu is open, remove all open processes by sliding the apps to the side.