A large part of being mindful is gratitude. Being mindful of the things and people in your life includes being grateful for them. There is no room for envy or jealousy.
Is it easy? No. It is easy to see someone living what you perceive as a better life and think to yourself "Why not me?" This is where being mindful comes into play. Be mindful of where you are now and where you have been in the past. Be mindful of the journey you have taken to get where you are today. And, more than anything, be mindful of the fact that, however someone's life appears, we can never know the true life someone lives behind closed doors.
Look at your life. Is there a roof over your head? Will you eat today? Have you at least one friend? You have so much, then, for which to be grateful. Be grateful for the multitude of blessings you already enjoy. Be mindful that you have them and treasure them.