Now into my third year of collaborating with teachers in designing PBL projects, I have seen a couple dozen projects in action and I've learned a few things in the process.
1. The driving question, the end task, and the learning outcomes are all interconnected. You can't come up with one without keeping the other 2 in mind.
2. Another set of eyes is crucial! PBL projects should not be designed in isolation. I, of course, believe that PBL projects should be created with the TL but I also think that an 'outsider' (someone from a different department) should also take a look at the project. If an outsider isn't enthusiastic about your project, your students won't be either.
3. Start small. I encourage all teachers to start with a small 2 day PBL project so that they can see how the structure works and taste PBL success.
4. That said, the best PBL projects I have seen are big projects, very big. I think that is due to the teacher really understanding what the big ideas of the curriculum are and the incredible amount of planning that has gone on beforehand.
5. Own it. Teachers should not try to find a PBL project online and try to implement it. A successful PBL project is one that you've put a lot of time, effort, and thought into. If you want students to take ownership for their learning, you've got to understand the intricacies of the project yourself.
Planning a solid PBL project takes a lot of time. Ask your teacher librarian for help, that's what your TL is there for. Ask your administration for release time. Make sure everything is in place before you launch because odds are, something unforeseen is going to pop up.
If you want great PBL resources, I highly recommend BIE's PBL books which can be ordered here: http://www.bie.org/store/ - the PBL Starter Kit is outstanding. High Tech High and BIE are great places to go to get ideas for projects. If you are on Twitter, you must follow Andrew Miller (@betamiller). If you ever get the chance to go to a PBL session run by Andrew, go. I've seen Andrew present 3 times in Kelowna and he is amazing. He understands the whole PBL package from curriculum to assessment and isn't afraid to tell you if you are off track.