Very important. Without putting much thought into who you are becoming in the world of Yliakum, you are... nobody. Just another random face with no interesting quirks or habits or curious features that will grab the attention of others. If you want to roleplay as yourself, that\'s perfectly fine (as my character, Karyuu, nearly IS me) but it still is important to think through to the beginning of your character, his or her early history, what made him or her the way the individual is now, etc. Once you do at, at least for yourself, it\'s much more fun to \'sink\' into the character. In the world of roleplay, you have the amazing ability to control every aspect of your persona - every movement, facial expression, and so on. You have incredible control, and you can use it in any way you like. However, without a sort of \'focus,\' that power is too broad to be used effectively. You have to set some sort of realistic and individual limits on your character. For example, create some intriguing likes/dislikes that will affect how the character feels towards others and make for good scenarios. Set goals for your characters, be they large or personal, materialistic or internal and emotional. Make them act a certain way because of who they are - not jump all over the place because they have no attributes that define them.
It makes things a heck of a lot more interesting :)