Ok, will try to comment.
1st, inconsistent output size, if you plan to use 640x426, then use it consistently, portrait orientation should be 426x640 and vice versa. Eg. #7/#8/#9.
2nd, White Balance, cloudy day doesn't necessary means cloudy WB, pics like #2/#3/#4/#5 is a little too warm. Since u r using a Nikon D40, u can try to +/- within the Cloudy WB to tune the WB. Sometimes you can try SUNNY or DAYLIGHT WB.
#1. overblown sky
#2. "chopped" limbs, can see one leg, cannot see the other
#4. framing, right side of model got "cropped"
#5. blown sky and busy background, snap
#6. cluttered background, watch those leaves growing out of head, eye's direction neither here nor there, watch those elbows
#7. blown sky, weird pose, "chopped" limbs
#8. bad background, weird pose
#9. floor cutting across model's head
#10. blown sky, weird pose, where's the models looking at? where's the center of attention?
#11. again, blown sky, busy background, and background does not add anything to the overall picture, better off showing the full body of the models then to cut them in half
#12. wierd angle, and most importantly, "can you see the models?
Most pics are either -2/3 underexpose to +2/3 overexpose. And I notice you are using manual mode. After the shot, try looking at the LCD and determine if the exposure if correct or not, all else, there's still programs like Photoshop, do adjust and correct the exposure/WB/framing before you post.
DP and others has pointed out the rest.
And lastly, don't give up, go out and shoot more, practise practise practise is the key. Look at other ppl's photos/gallery, and there's many web resources which u can learn from. The more experience u accumulate, the better you should be.
Just my 2c.