Regarding the sim, there is no one size fits all answer. If you fly short haul on a Boeing type, just doing some raw data flying and armchair prep will leave you fine. If you fly the 320, raw data might also be enough (it was all my sim partner, who passed, did) though equally reminding yourself what thrust levers and the trim switch do might also help.
If you are flying long haul, I would imagine some specific sim prep for a high workload raw data manual flying exercise would be a very good idea. We are generally judges of our own strengths and weaknesses on the flight deck and you will probably know what's best for you.
If you are flying a turboprop the whole thing will probably feel like a rest cure, though if you are worried about a slippery jet a sim might help boost your confidence.
They are not necessarily looking for "improvement" as such, but I was told in my briefing we were being assessed on:
- flying ability
- command potential/decision making
- trainability
Best of luck!