... You need a long term goal (I always go for something that just won't happen so that I ALWAYS have something to RP so I don't get bored when PK is low or something) For example Zubi, scion assassin had an elaborate plan to full fill the Scion prophecy. On paper it looked doable and I could full fill several steps of it. But would the imms ever really let the scion prophecy full fill it self completely? ;)

Short term goals... Religions, tattoos, joining a cabal, becoming a leader, killing some certain powerhouse enemy or whatever. :D

The progress of these things can be explained in updates, and perhaps the adventure it'll be to get to these goals makes the char change over time etc...

In the intro role I usually try to sum things up in a final entry stating things like: The events that have occured in the past has made "randomchar" start hating giants. (Of course then there is some event in the intro role that has to do with this.)
I basically list a few things. Likes, dislikes, possible goals etc. And not in a story-telling way most of the time.

Now... I've never won a role contest, just been a runner up... Once... But I constantly get decent imm-xp for my intro roles and role updates. (Say 1500ish for intro and 500-800 for updates.)

Or this wasn't what you asked at all? ;)