So, my perspective from the inside:
- offices either have a specific opening that they're hiring for, or they take rolling applications (for ex, SDNY and DMass do the latter). If they take rolling applications, they'll say so on their web site. If they don't take rolling apps and there are no current job postings, there is no point in sending in a resume; there's nothing to hire you for. If they take rolling apps then of course you can apply whenever you like, though I don't know how frequently they review/interview/hire.
- specific openings will be posted on USAjobs or at
https://www.justice.gov/legal-careers (follow the links on the right-hand side).
- my impression is that DMass is kind of SDNY-lite - very snooty and into pedigree and connections. Your pedigree is more than adequate, it's just a very competitive office.
- NH, ME, VT, and RI are probably somewhat less competitive (there are probably more local school grads/former state prosecutors), but they're small enough that the difficulty is going to be finding an opening to apply for. CT and NJ are big enough that they may be better in having more openings, but they're going to be more competitive by virtue of being closer to major major metros. My small office gets a couple hundred applications for an AUSA position. Full disclosure, a decent chunk of those applications are mediocre to terrible, but there are still lots of great candidates - and I'm sure we get low numbers of applicants compared to many offices.
- connections aren't required, but they definitely help. I think if there's an opening in a district where you have connections (people who you know, know people in that district) it's totally fine to have your connections call. Cold calls would be a bit weird but if Joe Partner is buddies with Jim AUSA and Joe Partner thinks well of you, I would absolutely have him call Jim AUSA to say you've applied and to put in a good word for you.
- consider asking your connections to set up an informational interview/networking thing where you chat with someone currently in the office about their job, to get on their radar. They won't be able to create an opening for you, but getting your name known before an application comes in is useful. And even if a job never opens up in that office, getting more info about the work from the inside is good.
- for the smaller offices especially (at least, based on mine), make sure you include a cover letter (weirdly, some otherwise great candidates don't) and make sure it explains why you want to be in that office. Pre-existing ties aren't necessary - though they help - but having some kind of answer to that question is important. It can be as simple as "I want to live somewhere my kids can go to good schools/with great access to the outdoors/lower cost of living" kind of thing, just something that acknowledges that you'd be moving and you're interested in committing to the area and answers "why is this person applying here?" (Offices like SDNY are not as concerned about ties/longevity b/c they have more of a revolving door with firms, to my knowledge, and DMass may be a bit like that as well - also access to outdoors/lower COL are more of a stretch for Boston obv!)
- highlight any courtroom/trial experience, but don't try to stretch it into something bigger than it is. USAOs understand that biglaw associates don't get to do much in court at a lot of firms. They're still interested in biglaw associates b/c they want smart people who can write and work hard. Of course sometimes you'll lose out to the local prosecutor who's done 50 felony trials, but if that's going to happen it's not going to matter whether you argued 3 motions in court or 4 - it's just the choice they were going to make.
- this is more amorphous, but be able to show that you've really thought about what a prosecutor does. Why do you want this job? In my office, because it's a stepping stone on the way to whatever glorious career is not a good look (we're filled with lifers. Again, some offices aren't like that, but the smaller ones will be). You have to convince them that you're truly interested in the work for the work's sake and that you've really thought about what it entails.