sorry to hear that you got the rejection letter but the best advice is to closely look at the prerequists and strenghen them. It is a good idea to contact the program director thank them for the experience of going thru the interview process and ask what you can do to make you a stronger candiate the next time around. Once advice is given, make sure you do what they suggested. It shows your dedication to persueing your dreams despite being rejected. And your not afraid of hard work.