Few of my points will be repeats of those from Siliverking, Woopty and others but for whatever they're worth here's a list of ten things I've learned over years chasing them...
1) STRUCTURE, STRUCTURE, STRUCTURE or said another way BAIT, BAIT, BAIT. And that's true inshore of offshore. Rocky outcroppings offshore are great as are all of the area artificial reefs, but so are inshore buoys, bird-racks, and any other objects that can draw / hold bait seeking to get out of the open. Highest number of cobes I ever saw congregated in one place was just outside the mouth of the Econfina at a bird-rack subsequently destroyed by Hurricane Dennis (and not rebuilt). Guessing it had 15 to 20 cobes circling it due to bait seeking refuge under the rack. That particular rack was QUITE close to shore.
2) Though might sound contradictory to the above comment stressing to fish structure, you CAN catch BIG cruising cobia in the open flats OFF of structure and shallower than you might guess. Have tagged and released over 50 cobia (boated over 100), and the biggest I've seen in our area swam within 3' of my stern while trout fishing in six or so feet of water. It was swimming in a pack of 3 or 4 cobia but the others were much smaller. We've seen enough cruising the flats we try to ALWAYS keep a pinfish behind the boat when drift fishing, and over time have moved from keeping it way out to keeping it only a dozen or so feet behind us. Farther we float it behind us, the higher the ratio of sharks we have hit to cobia. Sharks don't generally seem as eager to quickly approach boats so keeping the pin closer cuts down a bit on the shark bite while not seemingly hurting hook-ups with curious cobes.
3) Chumming works BUT isn't always necessary. I would attribute chumming to less than a 1/4 of the fish I've caught and structure or blind luck to the other 3/4. If I find lots of bait at the spot I'm targeting I hold on the chum, as we often quickly get bites without using it. I use chum if either I don't find much bait present OR if we've had a good bite but it's slowing (often due to solunar influences). I do find the chum often will turn the bite back on, even if just for a short while after it initially dies down. I often just use cans of jack mackeral, tuna, etc, with some holes jabbed in the cans as my goal is just getting some bait to come to me. Sure chum blocks would work a bit better but the cans are super convenient.
4) To Silverking's point, ALWAYS have an extra rod at the ready with an eel-jig or SPRO jig head with a plastic curly tail attached to drop near trailing fish or the crazy ones that just swim right up to the boat when nothing else is hooked. If there are two people on my boat the MOMENT someone gets a bite I do my best to be sure that a free hand gets the jig rod ready to cast if a trailing fish comes up. My best estimate is that about 1/2 the time trailing fish DO come up along with the hooked one.
5) Also be sure to cast jigs close as you can to any large turtles / rays that come by, be it offshore or inshore. Cobia love cruising around with them and I've seen more than a couple of well placed casts to turtles and rays result in bites from fish we hadn't spotted.
6) You can use frozen bait or live bait. I actually got hooked on cobia while trying to get into the grouper game, catching numerous cobia on frozen cigar minnows and frozen spanish sardines. Over time I found that mid-sized to large-sized pins gave me the best cobia bite while lowering hits from other species I wasn't targeting. With live pins hard to come by after the grass kills in our area last year we returned to using more frozen bait fish and still caught plenty of cobes, though do think we caught more shorts due to more slender profiles of frozen bait fish.
7) If offshore, I use a fish finder rig pulled two or three feet off the bottom, dropping to my egg sinker hits and then lifting enough to account for my leader length + 2 or 3 additional feet. May lift it a few feet higher this year based on Woopty's comment, not because I think cobia won't take bottom baits (they do so readily) but because keeping baits on the bottom makes for more nurse shark and goliath hits that while exciting, don't put my preferred species on ice. Also probably help just a hair on lowering percentage of quick cut-offs.
8 ) If you're on great structure but are biteless while watching macks, blues, jacks slamming bait 1/4 mile away, don't hesitate to pull anchor and go to the action. The cobia may not be the main culprits in attacking the bait, but as opportunistic feeders they'll join in around the edges of the feeding (much like sharks will too) and take advantage of the easy pickings.
9) If over structure, the name of the game after getting any bite is UP, UP, UP and unlike with grouper, getting a nice sized cobia to the surface once is far from a guarantee the fight is over, as I've had bruisers do the up and down dance a dozen (or more) times. ALWAYS BE THINKING "UP!" as failure to do so can result in countless cut offs. Trip out with the highest number of solid bites last year actually resulted in ZERO fish brought in the boat. The big ones don't get to be big by being stupid and often will target structure until you have them pulled over the gunnels.
10) Be careful about catching cobia fever. Darn ailment can plum slap ruin you on other fishing! I targeted reds & trout before catching the cobe fever and on those days when I sit biteless for hours praying for a single cobia to show I remember wistfully the days I pulled countless trout and reds in the boat on shrimp under cajun thunders. As with all other fish it's still called "fishing" for a reason versus "catching." More than once I've gone out on consecutive days to have the cobia bite on fire without any chumming one day and the very next day be completely dead regardless of the amount of chum used with bait seemingly gone from the sea.