Vikings did not have reliable written maps or accurate tools such as compasses to help them on their seagoing voyages, but they were able to navigate using a system of narratives, climate and weather knowledge, landmarks, memory and chance. There is evidence that they may have used primitive tools such as sundials to help with aspects of navigation such as determining latitude, but this is more of a theory than a verified fact. Astronomical advantages such as the reliable position of the sun, moon and stars likely helped Vikings navigate around the northern Atlantic Ocean, but given how many Viking shipwrecks have been found over the years, it's safe to say that their seagoing missions were not always successful.
Stories and songs may have been important in helping Vikings get around; even the reliable sun, moon and stars could be obscured by clouds or fog, meaning that these ancient people, who did not have much in the way of a writing system, would need some other way of knowing where they were headed. Stories brought back by other sailors could be turned into easy-to-remember rhymes, which may also have helped when the skies were hard to read. Many of these sailors seem to have had good instincts for weather as well, choosing to delay departure for seemingly optimal weather conditions to ensure a shorter duration at sea.