I feel like the effect of curses is often one of psychological terrorism - it’s almost worse to know that you have been cursed, and dread the outcome, than it is to suffer the effects of the curse itself.
I’d play up the fear, the dread, the terror. Have people exaggerate their fear, spread rumours, tell stories about what will happen. Play up the reactions of the people cursed as well as the people around them. Someone who is cursed might not die for many years, but perhaps their fellow villagers start to shun them immediately. Everyone turns their backs and never speaks to the person again.
Attach, to each curse, some “early signs”, which take place almost immediately, and tell you that the thing has worked. A small, conspicuous mark or sign of some sort - a white lock of hair, a tooth falls out, etc.
Otherwise, a small flash-forward, vision, or even simple narration could be enough. “You leave him there, standing in the clearing, knowing that over the next three years his hair will fall out, his teeth will yellow and rot, and that the entire village will never speak to him or trade with him again - knowing that his life, as he knew it, is destroyed.”