If you have any bad habits around thinking of yourself as "evil" I would make habits to correct them? I use to badmouth myself and for a long while, when I'd catch myself thinking something negative I'd yell to myself "SUPPORT!" and three guys in togas would come running through from somewhere around my left ear with a Corinthian column and set it up in the middle of my head
I finally got so I didn't put myself down anymore. About the same time, my middle name was "Danaher" and I renamed myself "Damnither" and that was a hard thing to break! If you can, think of fun ways to correct bad habits; it makes finding them and reminding yourself easier.
I take any self harm thoughts to their logical conclusion; what could happen (pain, infection, scars, disability, others who might be disappointed, me being embarrassed, etc.) and that can help me some. Otherwise I make fun of them, as they're just thoughts and I'm the one in charge (nah, nah, nah, nah, n-a-a-h! :-) My thoughts can't become real unless I make them that way.