Bumping to see if anyone has experience with rank lists/matching as couples in this situation
My wife (peds) and I (EM) couple's matched together 4 years ago. We were both very competitive for said fields. We each interviewed at ~20 programs (0verkill...but hindsight is 20/20) in a diverse geographic range. I matched at a 4-year program. She is moving onto fellowship after a chief residency year and I am moving on to attendinghood in community practice. My $0.02:
1) Be kind to each other. Making your rank list is stressful enough as an individual and now you have an SO to factor in too. Have a lot of discussions. Find out what's important to your SO. If there's a place that they will absolutely be miserable, send it to the bottom of the list without further questions asked.
2) It's all about location. There's so much regulation through the ACGME that pretty much every program is the same. For EM, Chicago will be more of a knife and gun club than say, Delaware. Believe me you will get the chest tubes you need to be proficient wherever you go. For Peds, some programs are lighter/heavier on ward/outpatient months. However, every program has the same base standards. Pick a location that has some of the stuff you like to do. I cannot overstate this - family is important. Residency is hard. Try to be within 3 hours driving distance of your family. I am grateful for being able to drive home for a long weekend when I have the time - this wouldn't be possible if I were on the other side of the country.
3) Make sure your training tracks line up. I trained at a 4 year program. My wife did 3 years of Peds and then Chief year. We lined up nicely. If you are at a 3 year program for EM, it's easy to add on a 1 year fellowship or a local attending year to match your SO. Non-EM specialties are harder to find shorter term things to be able to line up with their SO. For IM, at my place it's pretty easy for them to tack on a hospitalist year after graduation. Other specialties may vary. The last thing you want is your SO to be heading to a far away city for fellowship while you still have a year left. Long distance is doable, but it sucks.
4) Limit disconjugate ranking pairs. Again, long distance sucks. We ranked long distance pairs way at the bottom. There were even a few permutations that we refused to rank because the distance was just too great and we figured we'd rather not match and have to scramble/SOAP to the same city than be apart for 3-4 years (If I had to do anesthesia/radiology at a lesser ranked place that would have been fine). I know couples that purposely ranked pairings that put one person in city X and the other in city Y (maybe 2-3 hours away) because they just HAD to be at that certain program. Don't put your professional life above your family life. It's stupid.
5) RANK EVERY PROGRAM. Can't emphasize this enough. Just don't be that person that goes unmatched because they didn't rank their home program. I know people who did this and they didn't match. What a stupid decision. Do you want a job or not?
6) Prepare yourself for the possibility that you may be disappointed on match day. The match is complex. Couples' match even more so. Throw in prelim programs and now it just gets ridiculous. Your main goal is to end up in the same location - everything else is a bonus. I know a couple who matched into the same (semi-competitive) specialty in the same geography - one at a top place, the other at a not-so-top (but still very respectable) place. They were both competitive on paper (at least I think they were...who knows...talk is cheap). It was a huge disappointment for the "lower" match and I think this was a major contributor to the long term relationship's ultimate demise ~3 years later.
Good luck. Match Day was one of the most exciting days of my life and I will remember it forever.