Mars shows what a woman is attracted to in a man. Being with a man who is strong in her Mars element, or who makes close sextiles with her Mars, makes the relationship much easier, and increases sexual desire and compatibility. For a man, his Mars is part of his masculine nature, so it is best when his partner also relates well with this element.
Mars Conjunct Neptune
Sexual fantasies in which you pursue your desires and work out aggressive or creative approaches are more likely and can take the place or share space with your actual relationships. Your goals are difficult to actively pursue, because for the most part what motivates the two of you when you combine forces lies in the realm of the imagination. When the Mars person is in conjunction with the Neptune person, you would better get into role playing or find some way to harness all that sexual creativity.