If you're lucky enough to have homemade, authentic tamales, the best way is to steam them (in their husks) over hot water (in a steamer basket) until the masa dough and filling is warm. Remove the corn husks, top with a sauce of your choice and dig in!  If you don't have a steamer basket, you can add a little warm water to a slow cooker or dutch oven, place a small wire rack in the pot, put them on the rack and allow to cook on low until they're warmed throughout. If you buy some from the grocery store and they're vacuum sealed in plastic, all you have to do is bring a large pot of water to medium-high heat, place the unopened bag in the hot water and allow them to cook 20-30 minutes.