Hey man,
I've been working on a teams Doc for a good year now, though because I'm switching back and forth between home and school (out of state) I rarely have a consistant partner to practice with. I've competed in a couple CT tournies though never with incredible success : P. Anyway, my perception of Doc in teams, as with anyone's, I suppose, is that it depends on the character you're partnered with.
Here are a couple main points that I feel are important to consider in teams with Doc
Pills are dangerous-- as a player who's heavy on pillgame, whether it be fancy movement or rapid spam, i found having a teammate took some real getting used to. It's surprisingly difficult to avoid hitting your partner, and one needs to make much more careful decisions when it comes to "getting creative" with pills. Defensive pilling, or spam pilling whenever there's an opening, is alot less recommendable, being that you can bean your partner and get them screwed up pretty bad. My practice (depending on the character) has usually been to fulljump over my partner if they're too close, and read the pill's trajectory so that I'm shooting over my partner for support. You have to make this clear and practice it a bit so your partner wont go running straight into the pills. Because FJ gives you better mobility and timing, I'd recommend using it more than SH in teams, because it's easier to avoid nailing your buddy. There's also some awesome team related stuff you can do with pills, for example pillsaving your partner, whether this be hitting them with a pill off the stage to help them get another Up-B or shooting pills toward your partner when they're at really high damage and fighting an opponent with low damage. This is kind of a last-ditch effort, but from time to time I've had a pill cancel their momentum after they would have been killed by a smash attack. If the opponent isn't ready to punish, it can work. Generally, though, too hard to really be feasible. Use pills less than you would as singles; just be more conservative.
Doc is a great "deal-sealer"-- In the majority of the doubles matches I play, I'm usually with a more heavy offensive character, and my main purpose as doc (especially because my pillgame is restricted) becomes as a gimper. Doc's cape, bair, nair, and pills make him great at screwing with folks when they've been hit off the ledge. I've noticed it's pretty helpful to get movement down with doc (especially wavedashing) and keeping an eye on the rest of the screen, so that if need be, you can detach yourself from whatever squabble you're in and finish things off with your partner's opponent. For example, one of my more coordinated teams is with a Link, who does alot more projectile spamming than I do, but as an aggressive player usually manages to skrah people off the edge, throw them, or by whatever other means knock them off. If timing permits, it's incredibly effective for me to be as aggressive as possible here, and leave the edge to gimp the opponent before he gets back. My teammate, meanwhile, can guard the edge to ensure I get back, or, in his case, bomb/skrah save me if I'm an idiot and go out too far.
Fair/Dsmash are a whole lot better-- In teams, most players tend to lose some of their speed and judgment; it's hard to keep track of so much going on, and smart players are always being cautious not to juice their teammate in the face. Because of this, though, people are often less capable of moving fast or avoiding what they might usually be able to escape. Especially on stages with platforms where there is even more of a crowding sensation, i've noticed that Doc's fair and dsmash (the latter, especially wavedashed or CC'd) can really hit hard (well, duh) and often. These make for fairly good crowd control, but since you can't be incredibly clean or precise with them, they should be used sparingly.
Jabs, grabs, tilts, Uair, Dair (nair) --- These more cautious moves are super important in my book. With Doc i can get in, smack an opponent around a bit, give them some damage for either you or your opponent to finish off. I tend to use these more often than pills in teams as opposed to singles, mainly because you have more control over where the damage goes. F-tilt, Uair, uptilt, and Forward/up-throw are really great for setting your partner of for combos, since you can get them off fairly easily and they often put your opponent in a precarious position. Again, you and your partner should practice/coordinate enough that you know how to set each other up for combos and how to tell if either one of you can or can't do it in a certain situation. For example, against heavier characters, doc has better luck setting up combos with his Upsmash at low percentages, etc. With regard to the nair, i'd use it a bit more sparingly. It can't really murk people or anything, but flying around with tons of nairs has never really done me a ton of good in teams. It can be a precise move if you're careful, but you can hit your partner and it can suck if you catch them at a bad time, so don't be too gung-ho with it.
Doc's other moves are obviously usable (namely F-smash), but not necessarily, in my opinion, outstandingly useful for teams.
Err..
So i hope that helps. : D