Reasons why your android phone may hang or lag and possible solutions to it

   The truth is, most of the android phones available in the market hang and lag alot after using them for sometime. Most especially phones that have below 512MB OF RAM and low INTERNAL MEMORY. There are many other possibly reason and causes:

CACHE AND INTERNAL MEMORY:

   If you are an Android user, make sure you clear cache often, manage your applications so that it does not store too much data in phone’s internal memory and refrain from heavy browsing or playing hardware heavy games. This should lead to less crash, especially in low budget hardware Android models with low processor/cpu.

   Android application has access that is equivalent to Windows registry style things. Various apps dump garbage and useless things in cache, which fills up phone’s internal storage (like hard disk) and phone becomes slower over time. Even if you install an app in SD card, it still
leaves traces in internal storage space due to android OS design.

TRY BOOTING INTO SAFE MODE:

   If you use a samsung phone, you can Boot into Safe Mode, which prevents all 3rd party apps from starting up. If the phone works fine, then something you installed is causing the problem. You can try opening apps one by one and notice when the problems comes back then delete or update the conflicting application.

TRY REMOVING OR FORMATTING YOUR SD CARD: 

   If you have an SD card inserted, you can try unmounting it in Settings>Storage, remove it, and reboot. A corrupt sdcard or internal storage can cause problems and make your phone to lag or hang. It's possible that one or more file is corrupted -Try to connect your phone to a computer and copy your files, then format your SD CARD/INTERNAL STOAGE and see if the problem is solved.

TRY WIPING CACHE IN RECOVERY MODE:

   Try booting into Recovery Mode and wiping the cache partition, which won't erase any personal data. Put your phone into recovery mode but instead of selecting Wipe Data/Factory Just select Wipe Cache Partition. When complete, then select Reboot System Now and see if that will solve the problem.

LOW RAM AND TOO MANY UNNECESSARY APPS: 

   Maybe, installing too many Apps might just be your problem. Delete unwanted installed applications and you will notice your Android phone manages apps and processes in the background just fine. If apps should use too much ram it's going to cause problems. I'm pretty sure if you get rid of those apps you'll also get rid of your freezing problems.

TASK MANAGERS/ TASK KILLERS:

   In general, Task managers of any type don't play well with Android versions above 2.3, and are completely unnecessary. You will have to choose between Having apps running in the background or a phone that crashes all the time. Android is a multi-tasking OS. It's designed to have apps in the background. The only "wasted" RAM is empty RAM. Running apps will use only as much memory as they needed. Having a bunch of "extra" RAM won't make them use more or run faster. "Empty" RAM doesn't save battery; every bit of every byte of RAM in the phone is constantly refreshed whether it's in "used" or not.

source; http://phonetweakers.blogspot.com.ng/2015/09/reasons-why-your-android-phone-may-hang.html