Spend two minutes each week (more if you prefer) thinking of three things you are grateful for that benefit you and without which your life would be poorer.  Then think about the causes for these good things.

Be creative with your gratitude to avoid habituation.

Positive emotions are associated with greater creativity, increased problem-solving ability, and greater overall success in life.  

This can feel silly or forced when you first start but give it a chance.   Research has shown that even forcing yourself to smile can put you in a better frame of mind.

Source: PsyBlog lays out the case for practicing gratitude for 2 minutes a week.