Which airline? Are you still in new-hire training? If so, they should have told you everything you need to know.

If this is differences training, then focus on those things which are different from the 200...

Profiles and Callouts are mostly the same, except for the flaps.

Know the big-picture systems differences, especially the switches in the cockpit and the flight director.

Know the limitations which are different.

Know the different memory items of course.

In my experience at two airlines the atmosphere at 700/900 diffs was more instructional than checkride, but you had to know profiles and memory stuff in advance. I have heard of people getting fired for showing up "cold" with no advance studying completed.