Well if your instrument skills are up to par, then situational awareness and not getting behind the airplane.

You're immersed in a big new airplane, with lots of switches and procedures and profiles and callouts, that you're not used to, with things going wrong, while hand flying approaches in an airplane that isn't necessarily a piece of cake to fly single engine. On top of that since it was us 2 new hires we had to watch eachothers crap as well, to make sure one wasn't unknowingly screwing the other by missing something.. it would have been much easier I reckon if it was with a Captain who knew what he was doing. But they did take under account it was 2 newbies flying together so they weren't as hard on us. That was probably the hardest part, at least for me. There were easier and harder parts, but at times it got to where I felt that I was barely holding on and staying ahead. And once you get behind, when you're new, that is no good.. hard to catch back up unless you catch a break in the mean time.