Strong knowledge of A&P is a must IMO, especially F/E, acid/base, cardiac, and renal. People that barely got by in A&P struggle in nursing school. I think chemistry is also important...
Best thing you can do IMO is to seek out opportunities every chance you get. Personally, I let my instructors know what I want to do, as well as nurses on the floor. I also prep well, have my crap...