What are a few important central values of early Greek society which are expressed in the Homeric epics?

The first set of values one finds in these epics are heroic ones. In heroic culture, aristocrats are expected to demonstrate physical prowess in individual combat. Displaying certain types of courage is more important than winning. For example, killing an enemy by shooting him in the back is dishonorable, while losing a sword fight while displaying steadfast bravery is honorable.
The Homeric culture is one described as a "shame" rather than a "guilt" culture. In other words, reputation (Greek: kleos) is enormously important. The acts of an individual bring shame or honor to the entire family. Thus Menelaus' insistence on retrieving Helen or Achilles' anger over the distribution of war prizes has as much to do with honor or saving face as actual desire for the women.
Hospitality and the bonds of guest-friendship are extremely important. One can see this in the Iliad when Diomedes and Glaucus realize that they are linked by bonds of guest friendship and thus cannot fight each other. Polyphemus in the Odyssey, on the other hand, is considered extremely evil due to his violation of the code of guest-friendship.