Almost all my characters have a portion of me in them. It can be similar beliefs and values, or personalities, interests, background...
Helps me to be able to get in touch with my characters and allow me to slip into their shoes through that connection.

Suggestions by others above me are useful in their own ways, too. Like Lady A sometimes theme song does aid me to get into the mood of the character, or like Poohead, making characters that I do enjoy playing as.