Every writer draws from life and one of the greatest benefits of creative writing is an opportunity to recollect, revisit, reflect. In fiction you could rearrange and reconstruct reality, something that life doesn't offer us, a grand opportunity in which each failure can be a victory, each sorrow a joy.
The greatest fiction, however, is less fiction. A memory of the senses can be shaped, sculpted and profoundly affect a reader when faithfully rendered.
Dialogue should be real and quite ruthless in the rendering. The only rule for rules in grammar is the clarity and the crisp emotional bond you expect from conversation.