Things I've learned (or tried to) in my short new career:
1) Ask for help when you need it.
2) But if you need help, do not appear to struggle because your reputation in the beginning is *very* important.
3) Do cases with your senior partners. Not only is it a great way to learn something but it eases you into practice.
4) Let them know when you have a tricky case; do not be afraid to discuss concerns with them. Its much better to admit up front that you are unsure about something than admit you made a mistake and now are trying to fi it.
6) Remember you are (often) practicing in a place where they don't know you and your personality. Jokes that would fly at your old residency/fellowship program may not in a new environment.
7) Never speak bad about a colleague, patient, etc. it will immediately be broadcast on the nurse's network about how evil you are. I learned this when I was worried that my plastic surgeon wasn't going to show up (which he had been known to do before) late on a Friday afternoon of a holiday weekend. It quickly got back to him that I said, '"I don't know where the hell he is" when questioned by OR staff about his whereabouts and of course, my comments were totally blown out of proportion to my actual anger.
8) Learn how to bill and make sure to check your receipts. Medical billers will often "write off" cases that they think are too hard to collect. No biggie if its a $55 office visit; a pretty big deal when its a $12,000 brachytherapy catheter insertion. Trust no one unless your mother does your billing (and even then she might make mistakes).
9) Do your notes and coding, etc. ASAP after you encounter the patient. Nothing is worse than trying to recall something about a patient 2 weeks later. Dictate if you can, have someone else transcribe if you can, but do it as the patient leaves you.
10) Enjoy the small victories. I made a diagnosis yesterday on a patient that 3 other physicians had missed (SVC syndrome). It felt great after a rough day to know that I am actually competent.

So admire your skin closure, or how you handled that chronic pancreatitis patient or whatever makes you feel better. Brag a little here on SDN (like I just did).
11) And finally remember, you aren't alone. If you joined the right group or have a good mentor and back-up, there should be someone available to talk things through with you, scrub in, etc. when you need them.