Join a gym, if you feel you look good, than you'll be more confident. Seriously, joining a gym is a must Saying that, you're not too overweight, and I think if you just shed a bit through running etc you'd have a curvy look which a lot of men find very attractive
Just looking at that picture and you're clothes, it seems like you don't dress very feminie, maybe you should lose the tights, or at least were see through ones, do not wear black skirts (it looks like you're going to a funeral). Maybe you should buy some slightly shorter skirts made out of denim, theyre very nice, or even jeans, both would look very nice on you. Also, think about getting a top without sleeves, or rather much shorter sleeves. The top you're wearing in that pic looks kind of guyish.
And remember, personality is the most important thing, open up a bit more and relax around people.