Recipes usually tell you to drain and rinse tinned beans before cooking them; but that seems a bit fussy. You might as well warm them in their briny, slightly slimy liquid, and drain them when warm.
Last night, making a side dish to go with sausages, I gently fried an onion and a chopped clove of garlic in some olive oil and butter. Meanwhile, I warmed through a tin of cannellini beans in their liquid. When the onions were golden, I drained the beans, and stirred them into the onions with a tsp of harissa. (It's easier to warm the beans in liquid than to drain them first and then cook them, dry, with the onions.)
Nigella Lawson's idea, of adding lemon zest to the beans, is probably good. They need a vivid flavour to perk them up.