I guess I can add the first mistake I've made here too!
I just got my A license and was doing my first 2 way without an instructor. The guy I was jumping with had a lot more experience than I did but is not a trainer in any way.
Pilot orders a 15 sec delay, the AFF instructor jumping before us (he was traininig another instructor, not a student) says to wait more like 19 secs as he'll be moving a lot.
I was in control of the exit and counted way too fast. Dive went well, we did 4 points and then tracked away from each other. Unfortunately for me, that meant tracking along the jump run.
I opened and landed. The AFF instructor gave me a talking to, apparently we exited too fast and I ended up opening 100 feet away from him and he wasn't happy.
Things I've learned, count slowly and make sure you follow the plan. Don't track towards jump run. Buy beer.