I will give you some ideas:

Be sure you understand indexes and the differences between them (specifically clustered and nonclustered, but not limited to just these).

Understand normalization and denormalization, the why's and how's (my experience, more on the whys than the hows, but ymmv).

Performance tuning, don't need to be an expert, but be able to explain how you would performance tune a procedure or slow database. Using past experiences in this area helps as you can demonstrate how you worked through a problem. Shows the interviewer more than just what was asked.

I have had interviews where I was asked to name DBCC commands i would use in some situations. I simply said I wasn't sure, that's where I would use Books Online to figure out what I needed. Don't think they liked that answer, but I'm not a fan of memorizing commands and syntax because that is what BOL is for, reference.