Another great place to start is LindenLifestyles, they have a couple of great Avatar Kits. The Jill in a box and the Jack in a box. They also have some great free hair.
I always grab the male freebies too. They can look really cute on girls. Here I'm wearing the female skin and shape, tank top and cherry bikini top and flip flops from the Jill in a Box and the painter pants and matix sunglasses from Jack in a Box. The hair is the Calla Freebies I'm so Preddy V.2. The red ball in the picture is called a pose ball. when you click on it, you take on whatever pose or animation has been scripted into it. In some places the poses and animations are very very naughty.
Ok, here is the tricky stuff. How to get the gumdangit stuff out of the boxes.
1. Right click on the item you want to buy and then click on buy. It will give you a list of what is in the box. Click buy.
2. Now look in your inventory probably under objects and drag and drop the box on the ground. (sometimes the land you bought a box from doesn't allow you to open it there and you have to go somewhere else to do it, that's a drag)
3. Right click on the box on the ground and click 'open'
4. Then click on copy to inventory. It might give you an error message saying you arent' allowed to copy but it will put it in your inventory or some such thing. Just do it.
5. Now you have a folder with your stuff and you can just right click on the things to wear them.