Themes are huge for stand out photos! Think about what you want the viewer to feel / think when they see the photo. Are you taking a picture of a shirt that has football on it? Think about taking the picture on a football field, holding a football. Little props go a long way in a picture.
Lighting is important for any photo. It determines the color of the image and how much detail your camera can capture. Both images above are examples of photos with bad lighting. The top image is a problem because the bright sky washes out the subject. If your eyes are straining to look at the subject of the photo that is a bad sign. The second image shows the shirt well, but the model is poorly lit. The picture doesn't have any "pop".
Lets talk about background. A good picture has a well thought out background. This can make or break the photo! A good start is to have either a consistent background (like the shale wall) or one that isn't a distraction from the subject of the photo. (notice the blur on the background and the focus is on the foreground and t-shirt)
Get creative with your photos. Try different angles that you don't see every day. You can have two pictures of the same subject, one shot from a familiar, chest level shot, and the other from the ground looking up and come up with a completely different feel of the photo. Shooting "through" something also adds depth and drama to the image.
Minimum Photo Requirements:
Min size: 640 x 640px - Most smartphones take much larger images than this, so if you have a newer phone you shouldn't have to worry about it.