I have read some books on casting spells and have successfully caster a couple with good results, but what are the repercussions casting a spell that does harm?
In Wicca, for example, there is the belief of the threefold law, a karmic system that states that anything you do will come back at you thrice, whether negative or positive. Some people believe that anything you do will only come back at you once. I, personally, don't believe that there are repercussions for curses at all (except guilt or the spell harming the victim more than you intended, for example).
However, if you are new, I would not recommend jumping into curses. Just because you have successfully done a few spells and read some books does not mean you are ready to start cursing people. Study for a good while longer before doing that.
There's really nothing bad that will happen. Magick is full of grey areas, so do what you feel is right. If your specific path doesn't have a list of rules to follow [Like the Wiccan Rede] I suggest making some based on your morals. Some people see love spells as harmful, while others see curses as acceptable. You define harm and build around that. Harm to some is seen as eating meat, so they became vegetarian or vegan. While I'm not saying you should too, harm can be many things if you stop and think about it.
But let's say for argument sake you curse someone just because. What might happen varies again based on your morals and beliefs. A Wiccan might fear the rule of three [good or bad you'll receive it three times.] Some would argue they would have 3 bad hits from karma from doing bad, personally I feel it will effect you mind, body and spirit [you'll be worried bad will come, your body will feel tense and achie, and your energy will be low] others might believe in regular karma and might expect something negative in return. You might also consider doing something good to contradict the bad [say you cursed someone so you donate to charity as a way of personal atonement]
Overall it's hard to say, take a step back and think of the situation from your moral belief. I had a friend who cast a death spell on a man who molested many people, he determined it was worth it even though he was kicked out of his coven, his wife left him and one other thing he refuses to speak about all happened within the year of him casting the curse. I'm not saying the same will happen to you if you do harm, but the universe has a way of dishing out reward and punishment, just comes down to your view.
