Just be who you are in your essay. I'm sure you are not obnoxious or you would not be  going to school for this career. The last  person someone wants to seek advice from is an obnoxious one. Just write what about this career you would contribute in your way to those people who are unbalanced in their lives that may need your assist them. I find that the best of best psychologist come from those who have a been there done that past. If you have that then write about it.