using simplicity 4070 because of the bust seams.
you should have a "front bodice" pattern piece that you cut out on the fold that basically looks like this. yours will have the straps and a different neckline, and probably a more extreme side cut line
this is the "front side bodice" piece that you should have as well. it's what makes the curve for your bust to fit into. it may not look like the pieces fit, but they do.
the pink is the side, blue is front. see how the corners line up? that means they will fit.
use pins! lots and lots of pins!!! start from the bottom corner(the corner that will be sewn into the skirt) and pin your way up. when you get to the start of the curve, make sure the edges of the two pieces are on the same line always! it will create a weird bubble or two for the bodice front piece, but dont worry about it. its just the fabric moving to the curve. when you have it pinned sew it down.
i used a bright blue so you could see it. follow the curve with the foot, and be slow if need be. also, where the seam is there will be weird bubble like curves in the fabric edge. dont worry about them. you havent done anything wrong.
Pull the seam taught and look at it! it's how its supposed to be!~ you can also clip the curve a bit, just dont cut your seam.
and this is how it fits when over a body. the bust seam falls in the middle of the bust and when you have the side and back pieces on, it becomes taught. the best tip i can give is to use a lot of pins. take it slow, and if this doesnt help you, i'm gonna have to go out and buy that damn pattern lol.