The best way to ensure you are receiving Aglet for every step that you walk is to have Motion Tracking turned on and to allow Aglet to always see your location.

Go to your iPhone Settings > Aglet > Motion & Fitness On > Location > Always

Otherwise the app needs to be running to count your steps as you walk to earn Aglet. It can be running in the backgound, as long as you don't flick up and close it.