Watch the weather reports and look for a potentially clear night which also occurs on a night listed as a public night at one of the observing sites. Before attending round up any materials you may want to take with you such as flashlights, star charts, writing materials, insect replant, etc. You should dress appropriately. Wear pants and comfortable shoes. You may be climbing some stairs, or standing on deck planks, high heels and skirts are not recommended.
Most observatories are open to the outside air.
So, if it is cold outside be sure to bring a jacket, coat, gloves, etc. Before you attend it may be a good idea to make one last check of the weather. If it has become overcast you may want to reconsider and try on a different night when you can see something. If it is clear then go out and enjoy the beauty of the starry sky. If a tour is given be sure to participate in it.