all other rotations will pale in comparison. j/k
the first ophtho book i ever read was called basic ophthalmology and it is put out by the american academy of ophtho and is in most med school book stores and libraries. it's a good place to start and gets you familiar with the basic eye exam and the most common eye diseases that you will see. i think the subject of books has been talked about before on other threads. re: specific advice? if you are really interested in ophtho, you may actually try looking through the slit lamp at patients yourself so you get used to the way a slit lamp works. also, see if you can picture yourself doing what an ophthalmologist does on a daily basis. and if nothing else, this is the one rotation where you get to practice looking in the back of the eye in almost every patient...even if it's just with the direct ophthalmoscope while your residents are using the indirect. you'll be suprised how many of your classmates will graduate with an MD degree and have never been able to appreciate a fundus. otherwise, enjoy and relax. g-surg will be much different!
good luck!