Gratitude is knowing that whatever we have is from Allah. 
Gratitude helps us focus our minds on Allah, something that has unfortunately become so difficult today on account of life’s distractions and attractions. Gratitude, therefore, corrects our perceptions by reminding us that everything that happens to us doesn’t happen because of its own volition and thus we shouldn’t take matters for “granted”. 

Allah says in the Quran: 
“And whatever of blessings and good things you have, it is from Allah.”
(Surah Al-Nahl 16:53) 

Allah also says, 
“And He found you poor and made you rich (self sufficient with self contentment.)” 
(Surah Al-Duha 93:8)

Therefore, let's us constantly remind ourselves of Allah’s bounties by expressing our gratitude to Him in prayers and at other times.

Reference:
http://www.iqrasense.com/muslim-character/the-blessings-of-gratitude-and-shukr.html