I'm sure others will jump in with much better info, but just starting with the basics seems to be working well for me.
Quadrupedal Movement (QM)
I've read on other posts that for strength training you want to add weight until you can only do 3-5 reps (if that was in a different context I'm sure someone will correct me). So if you can only do one then the pull up is probably going to still be a great way for you to build strength.
What does that mean for a workout? Well, I would suggest doing three reps of one pull up each. If you still want more you could do negative pull-ups afterwards to further push your muscles, but if you're too tired to maintain good form then take it easy so that you don't hurt yourself. Listen to your body always.
There are some great stickies on building your workout program that I haven't made it all the way through yet so you should probably also read those as they have great information.
EDIT: Recent posts on training to failure have educated me on the pros and cons of it, with the general conclusion that in parkour training to failure is not beneficial. Instead of scaling back the exercise as you get tired (as I suggested above) you shouldn't push too hard unless you plan to rest for multiple days. Glad to have learned this tidbit!