If you have a slow Internet in your smartphone then this is the only way to improve your speed significantly!
Requirement: Any rooted Android phone, 2.3+
Download: 3G/4G Optimizer
Open it, grant the root permission and set the value to any options you like (Fast Upload/Slow Download - Fast Download/Slow Upload - Max Speed)
Then click apply and wait for a moment or until App become responsive then reboot.
If your a bit expert then set the values manually...