Thanks for the feedback everyone.
The hot knife is just a wood burning kit I bought at Walmart for about $25. If you are going to buy a set make sure it comes with an attachment for an Exacto knife blade. (It should come with several points and one of them will look just like the end of a regular Exacto knife) I put in a #16 blade and used that to score the lines in the plastic. When I did the front glacis and the area between the road wheels I did not mark vertical lines on the model before I started. I thought I could eye ball it and have it be okay. It wasn't. I would highly recommend drawing vertical lines before you start to get consistent horizontal spacing. I put marks every 4mm along the top edges and then drew vertical lines down the side of the kit using a machinist's square. (I think an index card would work just as well.)
You can see the pencil marks along the top in this pic:
As far as scoring the horizontal lines is concerned all I can really say is practice on a scrap model for a while.
One other thing I did learn was to let your hot knife heat up as hot as it is going to get before you start if you aren't using a rheostat to control the temperature. If the temperature of the knife increases while you are scoring lines the depth and general appearance of the lines will change. To get consistent lines while scoring you need to try and use the same temperature and pressure. You can't do that if your knife is heating up while you are adding the zimmerit.
Hope this helps some. Again, I am by no means an expert but I am ready to try it again. I only took about 2 hand cramping hours to do both sides and the lower front hull, which is the bulk of the work.
Shaun