Is running the best thing?

well I'm not fat, but I'd like to get toned. I like the shape of my body as it is, and I don't want huge bulky muscles. I just want to make my legs slimmer and my stomach flatter. I don't want to lose my boobs though, and I know that you do when you exercise. so is running for half an hour along with fifty sit ups good to do everyday?
Is running the best thing?
Post Opinion