#1. subject is centered as someone else pointed out. Also the background is really distracting.
#2 and 3 are sharp, but snapshotish
#4 best shot of the set. Good depth of field and interesting subject
#5 Centered and distracting background, lighting is also uneven, looks like on-camera flash perhaps...
#6 Better exposure in this one, but to keep from casting hard white light from the flash onto the subject, try wrapping a piece of tissue around your flash with a rubber band to diffuse the light. Busy background too...
Good start and keep shooting. The best thing you can do is know your camera and what it is capable of, so make sure to read the manual too. I'm a tad harsh on distracting backgrounds, particularly because that is an area I struggle with when shooting. I always forget to be aware of what is going on in the background... Anyway, keep shooting, and keep posting...