First, you should check whether the space on your Android device receives sufficient. Even if you sometimes still several hundred MB of available memory is, it can still cause problems.
So go into your Android Settings -> Applications. There, you can now find the device memory. If you wipe left you come to the internal memory, and finally to the RAM (memory).
If you notice that the bar is already filled to 80%, so check whether you can move something from the device memory to the internal memory. Otherwise, just uninstall some apps times. If you press the Menu button or the top right of the 3 points (depending on the Android model) so you can also sort by size.