If you get more specific, you’ll get better answers. You are not real specific here, so I don’t know if we are talking emotional and verbal abuse, physical abuse, rape or one of the other numerous tops but…
If you really want to make them suffer, spend some time making them feel like they are worthless, no one loves them, no one will ever accept them again, etc etc etc… Here is the technique I’ve used, and it wasn’t for abuse, just for ending someone by their own hands.
I aimed the topic at a different audience, but affecting someone energetically like this, is probably the most effective baneful magic I’ve used, even if I don’t really care to post about baneful works. I feel like we get plenty of those as is.
How to use this method for what I’ve described, should be plenty self explanatory if you read over it and the other replies 