Guitar shot. Veto on the selective color. His white pants fooled your camera into underexposing the rest of the image. He and the guitar are angled away from you. So you need a smaller aperture to get it all in focus.
Girl in the shade. If you're going to take a picture of somebody in the shade, then make sure the background is not in full sunlight. It just blows this image away. You've got a post from the chain link fence growing out of her head. The harsh light coming from the sides does not do justice to her face. Either use a fill flash or get her in full shade.
Pool shot. Harsh noon sun is not your friend. Try this shot again when the sun is lower in the sky, say around 6 pm. You'll be amazed at the difference.
Grandma's red hat. Yikes! That sure is a red hat. Get them out of the sun. Again, watch your background. Uncle Ned's armpit does not add to the charm of this shot. Also, ditch the blue cup.
Having a fancy lens is perhaps the least important factor to portraits. You need to develop a keen sense of lighting and surroundings. This will make more of a difference than buying a $1500 lens.
First lighting hint. The sun is your friend at exactly two times of the day and seldom at any other: the golden hour just after sunrise and the one before sunset.
