First, decide where you want your character to come from. This means not only their place of origin but their social standing, and religious affiliation. These items have an impact on the personality and other traits of your character. They can also influence your character's physical appearance.
For instance knowing where your character comes from gives you important clues to his or her cultural background. How a person dresses and the ornamentation they wear, including tattoos, may come about because of cultural beliefs and place of origin. A Suel from the Thillorian Peninsula will dress differently than one from the Tilvanot peninsula. The one from the Thillorian is from a cold, wild land, and his people's customs are considered barbaric by more civilized southern societies. The person from the Tilvanot comes from a highly regimented society in a sub-tropical land. Therefore, the barbarian may wear furs and bear ritual scars appropriate to his culture; while the Suel from the Tilvanot is more likely to wear light, voluminous clothing suitable to his climate. Their speech and mannerisms are likely to be vastly different even though they are of the same human sub-race.
Your character may have some strange taboos or superstitions based on his upbringing, such as a Baklunish warrior who believes that he will lose his strength should a woman ever view his bare neck. This will greatly impact this characters interaction with others. Or perhaps your character had been stripped to his skivvies by a party of elven nobles in his youth and hung from his ankles in a tree. He or she may either avoid elves or be extremely rude to them as a result.
Specifics of your character's history may also be reflected in his or her description. If you have ever seen the Princess Bride, you may remember Inigo's scars. The scars are likely to be mentioned in a description of him, and may cause questions as to how he had come by them. This is a terrific example of how a character's description, when written properly can lead to quality role-playing.
A down on his luck adventurer is far more likely to have worn and shabby clothes than a famed mage who is well regarded for clearing out a pack of wyverns. The current position your character is in and how he or she has come to be there will be reflected in the items your character carries and the quality of those items.