Most of the bands I record now are emo/screamo type bands so I'm becoming really familiar with the genre. In fact, I picked up a few albums that I liked based on some of the stuff the bands gave me as sound tests/examples. There are a few decent bands in any type of music actually... although sometimes you have to look for 'em.
Anyways, about recording emo bands.
Generally I find that there is less distortion in the 'typical' emo guitar sound than... say a metal band. If there is a lot of distortion it shouldn't be as tightly compressed (or compressed at all) as a metal guitar sound--and there should be more mids prominent. Do not 'scoop' the guitar sound of mids... it will not sound very emo if you do that. I like to run some compression (MXR Dyna-Comp) before the distortion pedal or amp to get a tighter sound that adds that 'edge' to the guitar sound that often works well with the sound. The added compression will, believe it or not, save your from having to put the amp gain much over 7.
For drums most emo guys want big, powerful and NATURAL sounds. Overemphasizing stuff with excess reverb, chorus or EQ will usually not be welcome if it can be heard. Big compression, however, is a must have.
Generally emo bands want a bright, fat and articulate snare. This can be the most challenging part of the entire recording process. The deeper rock snare, like Dave Grohl, generally isn't acceptable. I find that a bit of a 1.2khz cut and a 7-9khz boost on the snare will usually approximate this sound. I've been experimenting with AKG 414's, MD421's, Rode NT1's and SM57's to try to find that 'perfect' snare mike for emo but haven't quite hit on a sure fire winner yet....
Kick drums should be full and punchy--almost a heavy metal type of kick but with a tad bit more tone. 100hz boost, 200hz-400hz cut and a 2.5khz boost usually gets you in the ballpark. Once again compress it pretty good. An AKG D112, MD421 or RE20 has gotten me some good kick sounds that emo guys liked in the past.
Overheads and high hats are pretty loud in a lot of emo. Anticipate the drummer to ride a crash cymbal a LOT and make sure to set your overhead mics appropriately. Beware of cymbal phasing. I try to keep my mics with at least 3-4' feet of overhead distance, run the pad switch if I have one, and run a stereo limiter. A *LOT* of emo drummers really bash their high hats and cymbals so take precaution! I've had great luck with SM81's and AKG 414's for emo drummers (standard stuff).
Toms should sound natural but explosive. Don't overdo the compression here because the 80's HUGE STICK sound generally isn't welcome. Keep them sounding fat and natural and you probably won't get any complaints.
In general emo bands will want a lot of compression... as most of the 'big' emo bands (Thursday, The Used, Finch) have VERY squashed masters and we all know that most bands generally copy their influences. You may have to fight them to not completely want to squish everything.
For bass guitar look for punchy and deep sounds. Ampeg SVC's seems to be the amp of choice for emo bassists. The bass is often fairly high in the mix adding a powerful bottom end to the guitars--don't discount this factor when dialing in your guitar sound. The bass will add to the layers (I recommend 4 or more tracks of guitar) of guitar to create that 'heavy but not heavy metal' sound emo guys tend to want.
Expect to record some clean electric or acoustic guitar on the typical emo session. Once again use a lot of compression. If you can borrow an Orange
AD30, Vox AC30 or Fender tube amp to use for cleans the band will generally prefer those sounds to whatever they are running. A slight 'bite' of clean overdrive is usually the clean electric guitar sound they will be aiming for.
For vocals, standard rules apply--best results with the best singers. The microphone that I reach for first and foremost for emo/screamo bands is the Shure SM7 without a doubt. It can handle the huge leaps in volume from singing to screaming and sounds good and fat. The vocals can be fairly 'verb wet as it isn't uncommon for some emo singers (Thursday especially) to have a lot of reverb. Once again, feel free to compress the hell out of the vocals to get the softer parts almost as loud as the screamed parts. Don't be afraid to let some 'errors' into the vocal to humanize it and make it sound real. IT IS IMPORTANT FOR EMO VOCALS TO NOT APPEAR OVERLY PROCESSED!!! It should sound authentic as hell--even if it isn't.
I usually have the singers do a 'singing' take and a 'screaming' take to get maximum attention to the parts. It also allows me to easily compress the seperate parts. A big production technique in emo is to layer a vocal line with the singing and mixed in the same line screamed at a much lower level. Sometimes it will be for just a word or phrase. Don't be surprised if an emo band requests something like this.
Hopefully this will help you out. Like I said, I record emo bands all the time and am pretty familiar with the genre. Just professionally it makes sense to spend some time analyzing/listening to the music a lot of your clients like. As it turns out some of the bands are pretty good if you come from a punk/grunge background like I do. Thursday, The Used, Thrice, Alkaline Trio, Finch and Glassjaw are notably good bands.