Any tips on taking good pictures?

I just received a Nikon D3100 for Christmas, with the 18-55mm lens and 55-200mm lens. I know a young girl who will be 7 in April (birthday party will be in April too). Her mom wants me to take some pictures of her so we can make photo invitations. We're planning on taking the pictures in mid-March at the local park. She loves going to the park to play and ride her bike. I'm really nervous about taking pictures because I'm not the best photographer. I really want them to be happy with the pictures too. Any tips on camera operations that would help? What kind of poses does she need to do? What do I need to take pictures of? Anything will help me at this point. I'm open for anything!

1) learn how to balance ISO, shutter speed and lens aperture.

http://camerasim.com/camera-simulator/

2) learn how to compose your images

http://photoinf.com/General/Robert_Berdan/Composition_and_the_Elements_of_Visual_Design.htm

http://www.photographymad.com/pages/view/10-top-photography-composition-rules

You are setting yourself up to fail if you get nervous and think you are not any good. Change that thought quickly. I'm going to give you advice assuming that you know nothing technically about photography.

Set your camera to shutter speed priority and set your speed to 1/500 sec. If it's cloudy outside you may need to raise your ISO but don't go above 800. If you need to go above 800 to take a picture, start slowing your shutter down in one click increments until you get to 1/250. Let the camera expose for you, it may be off a little but you can still fix the shot. Under 1/250 you run a serious risk of getting motion blurs with a moving child.

Take your pictures in the first or preferably the last 2 hours of the day. Expect the kid to last 20-30 min at most. Don't be afraid to put the sun behind them. A cloudy is okay too.

As far as posing goes. I do not think you should plan anything, just go out and ask the kid to have fun. When you see something you like, work around that for a while and move onto something else. Make it fun for the child. If you are struggling with a stiff child, have them run. You can put the wider lens on at around 25mm and run next to them and fire away. A child will always laugh when they are running, they can't help it. The main thing is to not to take boring, static pictures that look like a run of the mill portrait person took them. You can look me up and if you like what I do, then follow my advice. If not, no worries, do what you like. It's your vision that is important.

Plan