How can I raise my chances to have a vaginal birth?

Good Nutrition. Good nutrition with appropriate weight gain is critical to having a normal size infant. Do the appropriate testing for things like gestational diabetes at the right time. Avoid early elective inductions of labor. Have a good line of communication with your care giver and know their philosophy of labor and delivery.
Depends. The healthier you are the better your pregnancy outcome will likely be. You should know that in america 1 in 4 women will have a cesarean delivery. That means you have a 25% chance of having a cesarean delivery. You will probably have a vaginal delivery, but be prepared for a cesarean section.