I love traits - and think they add a great deal to the game. You can use them in several ways... either to augment and improve what you already do, or to add something different to your character.
I'd think about their background and look at some traits that fit, likewise consider traits that might improve on their stealth or ones from whatever race or region they may hail from [adds colour to the character].
If the character is one you've been playing for a while then they'll probably have a decent history and background. Dig around at some traits that might fit, or add something fresh to an old friend :)
There's a complete[ish] list of traits Here and Here
If you fire some more info on your character up [race, short background etc] I'm sure some of us more familiar with particualr traits can help :)
