For me the toughest thing has been the sheer volume of stuff to learn:names,sizes,locations and different varieties of hundreds of sutures,dressings, instruments,instrument sets, etc. Different setups and patient positioning for each procedure. Different Doc's preferences. Tons of new staff names to learn. It just goes on and on--I used to tell people it was trying to drink from a fire hose.
Virtually NONE of this will be what you learned in nursing school or on the floor either. I had a BIG advantage since I was a practicing podiatrist for nearly 30 years before I went to the OR so I already knew about sutures, many of the instruments and also had working relationships with quite a few of the surgeons who I had shared patients with. It has STILL been a lot to learn.
On the plus side, I've had the time of my life this past year! I just love the OR and can't imagine working just about anywhere else.
Be patient with yourself and don't expect to know everything right away. Ask a LOT of questions! Talk to the other nurses, the techs, anesthesia staff, the Docs (most of them won't bite

).Be prepared for a really rewarding career.