How to make a professional fashion sketch

Hi
I'm a fashion designer and i have to prepare a good portfolio to get in a school.
this is what i do www.daniel-soliani.blogspot.com
as you can see the outline made with pencil is really bad and i would like to make it white or silver by using the layers, as somebody told me. but i don't know how to do it when i create a new layers it doesn't let me do anything on it.
can anyone help me?
thanks
Daniel

What are you trying to do on the blank layer? You can do stuff on the blank layer, make sure you have it selected when your working on it and not the background layer. You can't use something like the magic wand though, it would help to know what your trying to do on the blank layer.