Realize you won't be able to do everything right off the bat, and you'll be slow at some tasks. Don't beat yourself up for it.
I agree, the mentor and/or preceptor can really make the transition easier (or harder, if they are not a good preceptor!). Remember your school training gave you a way to think, and you'll always have that, no matter what the task. Remember, basics really are important! Take your time and think things through. Smile as much as possible, even when you are nervous inside. Every day, I think to myself, "I am going to learn something great today". That gives me a mental framework for starting my day, and I've been surprised how much that little saying can influence my ability to be calm and take things as they come. As others have said, ask questions. Lots of them! If you find a nurse who doesn't like your questions or sighs, move on and find someone who can answer them in a patient way. Never pretend you know something you don't; your patients depend on you to do the right thing for them.
P.S. Every once in a while, look down at your ID badge, see the "RN" after your name, take a deep breath and smile. You made it!