Oki, here we go :3

1: Try searching for gun references. Her thumb should be lower down the handle. The handle should be resting comfortably on the soft flesh between the thumb and index/trigger finger.
2: The gun he's using is a bigger hand held weapon so should be a little heavier. The way his wrist is angled, he'd have muscle pain in no time. His hand should be fighting against the weight of the gun.
3: Others have been talking about small feet and uneven knees. If you want her to have small feet (like my friend! D: SO VERY SMALL!) then, that's alright
but her uneven knees are a different story. If you wanted her leg to be a bit folded and behind her other leg, it might work; you'd just have to make her feet move back a little bit. Either way, you'd still have to fix the legs.
4: Unless her jacket was pinned to her shirt, it should be slipping down her side. So one side is longer than the other. Although, if her jacket was bunched up on her waist by her arm then the jacket would be the same length. However, the jacket would still slip a little.
5: His shoulder should be a little wider. His head is a little too big on the shoulders you've given him. His chest needs to be a little wider to make his torso a little balanced.
6: His left leg is thinner/smaller than his left leg.
7: His feet seems to be on the same level meaning that he's stepping on his feet. Also, the girl is stepping on his foot. To fix this, you can shorten his legs and draw his feet just behind hers.
Also, use rulers for straight line!
biggrin Also, think about how close they are to each other and to the objects around them :3