I started by doing a small amount of research on the internet. I was surprised by the amount of information available. Since I was planning a kids party I found this site to be helpful for gathering ideas. http://www.birthdaypartyideas.com/html/harry_potter.html As I saw ideas I liked I copied them into Word. I saved webpages in a Harry Potter Party Folder so I could return to later as I quickly found it was easy to lose information, in the vast plethora of what was available, that seemed easy to find at the time. I also saved images into a separate folder that I thought could be useful down the road.
I also found it helpful to see pictures from this woman's website and that in part inspired me to create a blog to share ideas with others. http://www.britta.com/hogwarts/index.html