The best bait I have ever used for live trapping coons is canned/wet catfood. The stuff stinks like crazy, and apparently, it smells dang good to coons. I've used it for over 15yrs, it's cheaper than sardines, and more effective (and doesn't seem to bring the skunks nearly as much either).
I put a small spoonful in a gatorade bottle lid, or a 2-4" flat jar lid (any tray that size would work) and slide it to the back of my traps. In general, I only handle my traps by the handle, so I don't put much scent on the cage.
How you place your traps is the most critical part. Be sure you're not scent marking the entire area around your traps, and be sure you're putting them in a high traffic area (for coons, not for people, obviously).