As a quick follow-up to Making it easier to submit papers to Usenix LISA, here's a tip for writing a good Practice and Experience Report: Work backwards from the "lessons learned".
Step 1. Write down the 4-5 things that you wish you knew before you started the project. That is, things that readers will feel they've learned after reading your paper.
Step 2. Work backwards from those 4-5 things to figure out what people need to know to understand them (for example, the story of how the project got started, the problems you faced, and how you solved them). You really don't need to include much more. The audience is technical and doesn't need that much hand-holding.
If you work out those things (preferably on a whiteboard or index cards) the paper will write itself. I prefer to start on a whiteboard because it prevents me from starting to write paragraphs too soon.