I like your style, it's simple and cute! I'm not sure how old you are (you are a beautiful, fresh face young woman). From what you posted, I would guess you were in high school (freshman in college at the oldest)...If so, I think you are dressing appropriately. Nothing to fancy or trendy. However, if you do what to change it up a bit, I suggest what the other ladies said, (accessories!! but not too many).
You have great basics, now you all you have to do is spice them up!
For example in the first pic, I would take off the pink sweater (and flip flops). I would rock the tanks with the jeans (no use of buying more stuff-LOL). You could add a some bracelets (and layer them), pumps (funky sandals or flats). Add a really cute color on the nails (a cheap fix).
Third pic: that black/white printed shirt/cami looks really cute! You could take off the purple shirt and rock the tank/cami w/the jean shorts. I would probably go with dressier shorts (darker blue (or white) trouser type shorts ) a long thin necklace, and cute flats or thong sandals...You don't want to do sleeveless shirt/cami, w/shorts and heels...
If anything, I think you might be slightly guilty of overlayering...especially in the last pic. I think you have on too much. To change the look of the last outfit, I would remove the lighter jeans (opt for a darker wash), flats (because they are boot cut jeans) and look a little long w/the shoes. If you want to do the flats I would look for a jean that has a more taper leg. And is that a shrug or cardigan you are wearing?