The best way to cook canned collard greens is the same way you would cook them from scratch, with smoked or cured meat like well-cooked ham hocks, pork shank, fatback, or bacon.
You'll also want to add some onion and garlic, but if you really want to cut down on prep time, substituting onion powder or garlic powder will do just fine.
A little bit of table or seasoned salt, some pepper, a pinch of sugar, a drop of vinegar, and something spicy like cayenne or red pepper flakes will also level up the flavor.
Start with a little oil or butter — the fat will help carry the flavor of the other ingredients and will coat the collard greens once they're in the mix.
Saute each ingredient to bring out the most flavor, and don't bother draining out the meat fat because it will only add to the flavor of your collard greens.