Well, when I decided what I wanted my goal to be, I started off by figuring out what a "normal" BMI would be for someone of my height. (For a person who's 5'2" the high end of normal is 136 pounds) I am 5'7", so I calculated my goal weight should be somewhere below 158 pounds. I settled on 150 and discussed it with my surgeon, who agreed that was a good number for me. This is what I have been working toward ever since.
Good luck with getting to your goal, whatever it might be!