It is important to have good previews for your products on TpT, but it is also important not to give away too much for free.
I started just putting "Preview" on my pages for a preview, but discovered that it is pretty easy for people to convert the file and take the "Preview" off. I don't know if people are actually doing this or not, but I like to try to help people be honest.
Some sellers create the collages with Picasa so that buyers can see all of the pages in the product. I have tried this to, but it just didn't work for me. It would take me forever to arrange the pages and it just never looked right. Plus, it was hard to see what was on each page.
Finally, I came up with a solution. I create all of my products using Power Point - it is so much easier to move pictures and text boxes around! When I am ready to make a preview I simply record my slide show. Each page is shown for a second or two. I then save the file as a .wmv file and it is a movie. Buyers can see every page in extreme detail, but can't grab any of the pages. Plus, as a bonus, it is easy to do!
Here is the preview of my Word Family Practice -am Words: