A mound of tasty greens goes well with just about any meal, but you have to pick the right greens for the job. If you want something you can wilt in a few seconds or saute in a hot pan, spinach is your friend. If you're planning to simmer a ham hock or country ham all day, collard greens are your best bet. They're sturdy enough to stand up to long cooking and they'll absorb lots of flavor from the ham, but sometimes that can be too much of a good thing. If your ham is extra-salty, your collards will taste pretty salty as well. That doesn't mean you have to toss them – just that they'll need fixing.
Sometimes, the simple fix for really salty collard greens is to just do nothing. Before you start frantically searching recipe sites for fixes, try a bite of your collards "in context" with the rest of the food that's going to be on your plate. They may taste too salty on their own, but just right with a fork full of potatoes or a slab of cornbread. That kind of full, in-your-face flavor is why you cook the greens with a cured meat in the first place, so don't be in a hurry to tone it down until you're sure it really is a problem.
Toss Them Back in the Bath
Once you're sure the collards need help, your best bet is to get them back into the water. Dissolved salt will always travel from wherever it's more salty to where it's less salty, which is exactly how the problem started. Salt was drawn from the ham, or whichever other meat you used, and passed through the cooking water to your collards. If you put the collards back into plain water, even if it's just for a few minutes, salt will travel back from the greens into the cooking water. Simmer them briefly, then pull out a fork full of greens and taste them. If they're good to go, drain them and set the table. If they need a few more minutes, put them back.
Provide a Distraction
If you and your guests are not actively monitoring your sodium intake, sometimes you can get away with masking the saltiness of the greens instead of actually taking it away. Basically you're confusing your taste buds, drowning out the salt with bolder flavor. This is pretty much what happens when a whole bunch of kids are shouting at the same time; it's hard to pay attention to any one voice in the crowd. Your best bets for this are tart acidity and spicy heat. Adding a splash of lemon juice or good vinegar to the greens takes away the perception of saltiness, and as a bonus, it helps cut the richness of the meat. Dousing the greens with a healthy shot of hot sauce does much the same thing. Most hot sauces are pretty tangy in their own right, so that acidity plus the sauce's chile heat gives you twice the effect.