Just like mixing everything else, you do not want to solo your snare (or turn it up way louder than the rest of your mix) when mixing, otherwise you'll end up with an amazing sounding snare that won't fit in the mix. I turn the gain on mine up a hair, but the key is to not overwhelm the rest of the mix.
Often (most) times, you will get at least two snare tracks: 1) snare up (snr up) and 2) snare down (snr dwn). However, I've gotten as many as 5, maybe 6, tracks intended for snare (snr up, snr dwn, snr trgr, snr smple, snr sub, etc). Provided I have more than one snare track, I run them to a dedicated stereo snare bus -- regardless of whether they were mono or not.
If everything was recorded well, you can often get a fantastic starting point just by blending the snr up and snr dwn tracks to taste (remember, just because they provide you with a snr smpl track, doesn't mean you have to use it if it doesn't add anything to the mix). If you can't get to a decent starting point with just those two tracks, bring them down a bit and try to start blending in the other snare tracks to see if you can improve your situation (if you have them).
If you only have one less-than-optimal snare drum track, or if you just can't get to where you want to be by blending the all of the snare tracks, it may be time to call in reinforcement. By this, I mean Superior Drummer 3 (SD3) or a similar program. The goal of this is to not replace the the original snare, but to reinforce the original snare by blending it in with the original signal -- whether you need more body, attack, or whatever, you can find it with SD3. The program has a ton of snares to choose from -- just make sure to strip off any post snare effects SD3 may have put on whatever kit you choose for your snare sound so it will sound cohesive with your kit when you process your drum bus.
Onto processing. The first thing I do is add a visual, parametric, multi-band EQ. This is the only entirely snare-specific EQ I use. I like the SSL Native X-EQ 2. Many people start with subtractive EQ, but I like to boost the sweet frequencies of the snare until I get the snare sound I like. This means a bit of a boost from 120-240 Hz and boosts at 900 Hz, 5 kHZ, and 10 kHZ. I alter the levels of each boost until I get a great snare sound. I also use this EQ as my high and low pass filters.
After this, I add compression. I've personally found the dbx-160 to be quite effective; however, I've used a CLA-2A, Fairchild 660, and some other compressors with equally good results. I'm a proponent of light compression except in the most dire of circumstances. I like a compression that will hit about -3 or a little less on most snare hits and will go absolutely no higher than -7 on the hardest of hits (if your track allows). If your track does not allow, sometimes I will double up two very light compressors in a row to get where I need to be.
When I'm finished with compression, I use two old school EQ plugins which I use to try to tailor the snare to the mix (bring out the good parts of the snare which do not conflict; attenuate any conflicting frequencies). First I use the Pultec EQH-2 followed by the Pultec MEQ-5. Remember, depending on at what point in the mixing process you EQ your snare, you may have to go back and tweak the settings a little bit if additional conflicting frequencies or openings arise. THEN, I may or may not use a simple three band shelving if I feel it needs a bit more bite
Sometimes... if I still do not have the sound I am looking for, I will use a saturator/harmonic distortion plugin. There are good ones and bad ones. I won't name any names, but I will say that the SSL Native Saturator is superb.
Now, some people will add an early reflection reverb to their snare, but that's a whole different topic which I may address later when I talk about drum bus processing -- it's really song- and mixing- style specific
PS: Way, way back when, I used to just use a visual, parametric, multi-band EQ, a compressor, then run it through something like Vitamin on one of their snare presets (tweaked a little bit). I found out early on that I can get a much better sound through this more rigorous method. There's no shortcuts to a great mix.