The best and easiest thing you can do to raise your learning speed is to make a habit of using the Extra Puzzles (sliding to the left to get another puzzle) whenever possible. Simply solve 2-3 puzzles whenever on every lock or loading screen (unless you are in a hurry, of course) and you will double or triple your learning speed.
If that is not enough, consider giving yourself more learning opportunities. Activate both, the lock screen and the loading screen add-on, if you have not already done so. Consider adding more apps to the list of apps for which you get loading screens.
If you use your phone to check the time, consider solving a puzzle whenever you do. The typical smartphone user looks at the lock screen 3-4 times as often as they actually unlock the phone.