I'm a forensic guy, so obviously a bit different, but I think the general principals are the same. I think the biggest thing is to know your limitations and don't be afraid to ask for another set of eyes or another opinion. Everyone gets a lot of leeway at the beginning. Asking for confirmation of you first few cancer diagnoses isn't going to get you any flak if you're in a good group. Messing up big early is bad. I'd also say to trust your training. If you're competent, you're competent. Don't forget that fact and think you know nothing. Differences of opinion and style are normal - don't take any disagreement personally, and don't assume you're wrong if you call a prostate cancer 3+4 and a senior person calls it 4+3. Maybe you are, and listen to the explanations, but don't just capitulate.
Last, and probably most important, play nicely in the sandbox. Be a team player, be normal and pleasant to work with. These little things have nothing to do with medicine, but make a big difference in the quality of the work environment.
mlw03 had some great points. One of the best pieces of advice I got was "When in doubt, send it out." While that could mean send it out for a true expert opinion, also take it to mean show things to others. The more senior members of your group should certainly recognize your inexperience and should be more than happy to give a second look to your cases. Early on you will show a lot, and soon enough you'll be comfortable with most cases and will only show the tricky ones. But remember, it's more important to get the right diagnosis than it is to preserve your pride. If you have even the slightest doubt about what you're going to sign out, see what someone else thinks.
Recently reached my one year anniversary in practice (mid to large private practice group with general surg path sign out). Generally agree with previous responses. I feel pretty lucky in that my group has a fairly conservative policy for intradepartmental consults/second pathologist reviews to begin with (e.g. all breast cores and all prostate cores, among a few other things, are required to get a second review before sign out) and everyone was very patient and respectful with my numerous peer reviews in the beginning. Don't be afraid to use the LIS to look up the way that your new colleagues like to phrase/format their reports - I found this particularly helpful for some ditzels that were obviously benign but I wasn't quite sure what to say about them and for scenarios in which you are trying to politely convey the fact that there is insufficient/non-diagnostic/non-lesional tissue in a specimen or the presence of results discordant with the clinical history to the clinician. Sometimes I found phrasings that I liked even better than what I had been exposed to during training. Our group also uses Dragon for voice recognition for dictating reports and we have a lot of canned comments and a few types of specimens that we have synoptic style reports for (in addition to the CAP's synoptics for malignancies in resections), which is also helpful.
Yes, it can definitely be frustrating when you get a lot of feedback regarding the style/format of your reports or disagreements over things that are very minor/subjective, but this seemed to taper off over time as my colleagues got used to how I like to phrase my reports and what changes I would or would not be willing to make in that regard. I tried to take a lot of that feedback from the mindset that the reviewer was trying be helpful/educational (which I genuinely think they were in most instances). Generally speaking, if the other pathologist made a really good argument about why they phrase something in a certain way (or do or do not list such-and-such pertinent negative or get stain x or whatever), I was more inclined to go along with them (even if the reason was kind of weird or just pertained to the preferences of the local clinicians/surgeons). To be honest, I also have one colleague (considered our in-house expert for a particular type of specimen) who is much more likely to make a fuss about the exact way reports for that specimen type are formatted/phrased and after a while I decided it just wasn't worth the hassle of having my style commented on (and often having good-natured, but sometimes lengthy, in person discussions about it) for each of those cases, so I now just do them exactly they way that person does.
As far as actual diagnostic disagreements go, it can be embarrassing to be wrong, but I try to remember that every time one of my colleagues picks up a genuine error, they are saving me from what could have been a potential lawsuit down the line and overall making our group better. Not sure if this pertains to your situation or not, but I had fellowship training in a specific organ system. So I tended to be be more willing to "capitulate" to the diagnostic recommendations of my colleagues in specimens from organ systems I am less experienced/confident about. I also try to be polite (e.g. acknowledge if there is some degree of subjectivity in calling x, y or z or if there is some disagreement between national experts, but those where I trained taught me to use blah, blah criteria) when disagreeing with colleagues and/or sticking to my guns about specimens that ARE within my area of expertise. I also discovered that, even though I did not do a fellowship in them, there are a couple of other areas that were very well taught in my residency and I happened to be more knowledgeable about than certain of my colleagues (in spite of their experience), so, in agreement with what mlw03 says, don't assume because you are new in practice that you know absolutely nothing.
Not sure what will help you in terms of avoiding "second guessing" your diagnoses. If you're genuinely not sure, it is very easy to find an excuse to sleep on it and put any particular case off for a day or two (submit more sections, get another stain, have another colleague look at it, read some relevant articles/textbook chapters) and, if absolutely necessary/appropriate, you can always send it outside your department or even express your degree of uncertainty in a well-phrased comment. I tend to me a bit more on the confident side, although that is not to say I am a total cowboy and I certainly still show a good number of cases around. Most of the time once I have made up my mind or been convinced by a colleague of the best way to sign out a case, I don't lose a lot of sleep over it. I will say that we tend to send out a lot more cases for an expert consultation in private practice than what I was used to seeing in my training at more academic places and it took me a while to get used to it. This comes from the fact that patients with particularly unusual or complex cases will often get referred out of the area to a larger regional tertiary academic center for further treatment (in which case they will be reviewing the case at that point anyway - better if we have their agreement up front, especially as occasional, less educated clinicians can take minor differences in terminology or mentions of not-so-relevant other minor findings in the academic center's report as evidence that we were "wrong" or "missed something"), as well as the fact that national experts are "allowed" to make judgement calls in completely borderline cases or make up descriptive terminology for odd scenarios.
Don't be arrogant - you are new, don't underestimate how much senior colleagues know, even if it's in your specialty, but at the same time don't be too deferential or cautious. You are right out of training, you know more esoteric stuff than most at that point. But lean on senior colleagues for things like thresholds, gray areas, etc.
Show things around, but don't show everything around. But if in doubt, always show someone. No one is going to fault you much for being extra cautious, but plenty people would fault you if you thought about it but didn't show anyone.
Understand your group and practice facility's patterns - don't overuse IPOX if you don't need to. Use the diagnostic style that they do (templates, wording, etc) but don't be afraid to suggest modifications.
Get to know your colleagues, and as important get to know the other people who work there - they can help you out a lot and maybe bail you out from time to time. Most techs and other workers have little patience for an arrogant aloof pathologist, but if you show them you are their colleague also that will pay off more than you think.
Get to know the clinicians who deal with the cases you are seeing. Introduce yourself, show up to stuff, ask what they need or what the group could do better, advice for you, etc.