There are many fad diets that have been purported to assist fertility; however, none are substantiated. The best rule of thumb is to get adequate caloric intake and maintain an ideal body weight for pregnancy. Both too high and too low weights are associated with reproductive difficulty. An body mass index between 19 and 28 is ideal.
Women attempting pregnancy should also be sure to get adequate folic acid intake. The amount in prenatal vitamins is sufficient unless you've had a previous baby with a spinal cord intake. In this case, more may be required.