This is a big question. Most religious writers tend to think that an atheist's life must be empty, bereft of meaning. This is not surprising, since most hold that God designed us to center our existence around him, so it could not be possible to live without him.
First, I would offer my own life as an example. I no longer believe in a god. Yet, I am not unhappy.
I have good days and bad, just like every theist.
I have goals and dreams, just like every theist.
I love my family and friends, just like every theist.
I do not have to seek to fill my life with addiction and distraction(although, since I have a very wide range of interests, I am sure it sometimes appears that way).
I recognize the fact that I am the only being responsible for my failure and success.
Micki had it right.