Your worms need 6 things to stay healthy: temperature, food, moisture, airflow, bedding, and darkness.
Temperature: Your worms need to be stored between 55 and 77 degree. During the hot days of summer you should keep your worm bin in the shade and during winter you should keep it indoors or in your garage.
Food: Worms are vegetarians so any garden waste you normally would add to your compost (expired fruits and vegetables, bread, egg shells, cereal, etc) you can give to your worms. There are some tricks to make the fruits/vegetables easier for the worms to eat by putting the food in your freezer for a few days and/or putting it in a blender and make a worm food smoothie.
Moisture: Lack of moisture is the easiest way to kill off your worm population. Like us worms contain a high percentage of water without moisture they will dry out and die. Most of the time the food you add will give your worms enough moisture to be happy but on hot/dry summer days you might need to add a little extra water to your bin.
Airflow: Worms need air to live, make sure your worm bin has air holes. You must also ensure that your bin does not get too soggy which can suffocate your worms. If you find your bin begins to get too wet add some shredded paper and mix in with the existing bedding. If you bin frequently gets waterlogged you may want to add some extra air holes to your bin.
Bedding: Bedding gives worms space to live and also allows area to bury food scraps. This also adds material to store some extra moisture.
Darkness: As long as your bin is created out of a opaque material and you keep a lid on it this one should take care of itself.