Andorians are somewhat akin to the Klingons, or the Vikings, from Earth's history. They are aggressive, and honorable, often living for the fight. They have their differences, however. Central to Andorian society is the concept of the duel. These duels are often formalized affairs, though they are not witnessed save by the participants, a group of three judges, and a pair of specially trained actors, who record the duel in a specialized notation, and can play it for others a year after the duel. The duels are used to resolve matters of honor, and are a outlet for Andorian aggresiveness, which threatened the Andorians with extinction hundreds of years ago.
Another central Andorian concept is devotion to one's family, both immediate and extended (which are formed into clans, known as Keths (singular Keth)). Spouses are considered more important than children, as throughout the annals of history, children often died before reaching maturity. Andorian marriages are an oddity, as they marry in fours. Instead of boy falls for girl, girl falls for boy, and they marry, it's somewhat different. The boy falls for the girl and vice versa, then, when they decide to marry, they find another couple who they love as much as each other, and the four marry. In some of the varied Andorian religions, the proper number is six, and this is considered legal, if somewhat unorthodox.
The key to remember when roleplaying Andorians is an overwhelming passion for everything they do. Other considerations are their aggressiveness, as well as their honor. Insults to one's honor are not, as it is with Klingons, an invitation to an all out brawl, but an invitation to duel. Andorians generally respect the military forces of the Galaxy, and accord a level of respect to military heroes akin to those 20th century humans accorded pop icons and movie stars. They rely not only on Starfleet, but also on the Andorian Defense Force, for defense from hostile powers. The ADF is among the largest non-Starfleet military in the Federation, and primarily concerns itself with anti-piracy operations these days, though. A few other traits many Andorians, though not all, tend to share are a fascination with history, a fascination with Vulcans, a fondness for the natural state of things (Andorian colonies are almost never terraformed), and few nudity taboos (Andorian lodging is often communal, with no private rooms). This also means that nudity has almost none of the erotic connotations that it posses in most cultures, and a severe dislike of large bodies of water.