Try not to think of a gimmick that will "work." Think of a gimmick that is an extension of yourself. I mean...Ricky was a fat pirate who talked to animals and zombies...he got over pretty well...mainly because I could feel it and identify with the character being displayed. It felt a lot like my inner world. In contrast, rWo Ricky was terrible, tapped into NOTHING that was within me, and it definitely showed.
Ideally, who do you want to be? What do you like about yourself...what DON'T you like about yourself? What do you despise in others? What things in others would you like moreso to identify within yourself?
Think about all of those things. Also, watch a bunch of old promos. Use those influences to help find your voice.