yoo your dress is good! not bad at all~~~ I am not good at tips really but on the tops of the sleeves if you cut down the like circled part to fit the model it would look more fitting? What program are you using :)
@Whisper ooh I see, sleeves are hard to match with the body, an easy way to make the shapes you want is to make a new layer ontop of the model and paint bucket it the color your want the dress and use the polygonal lasso tool to cut it out. If you cut out the shape then slect inverse before you cut it though or you will just get a light dress shaped hole lol but I think your sleeves look fine~~ you just asked for some tips and that was the only thing I could think of